Well...there are a lot of things in this thread that are really misinformation and I'm going to try to clear some of it up.
First-the VF40 and VF46 share the same CHRA with an 8mm shaft, journal bearings that are 12.355mm OD x 7mm wide, and the piston ring end seals that are a bit inadequate but if they receive proper oil, they will last a long time. There is not one thing wrong with the VF40 and VF46 except for the maintenance done on the rest of the engine by the owner, and because of the improper maintenance, the oiling system not fulfilling it's duties to get the oil to the journal bearings. If all the lines are clean, good oil is used (yes, even some DINO oil is good enough if OCI are proper and consistent and good filters are used) along with the proper filters (blue Subaru, black Subaru, Roki Mazda, Amsoil 25K-these I KNOW have the correct check valve in them) and the banjo filters are removed (another Subaru MORONIC innovation designed to blow stuff up), there is no reason that for all practical purposes, the turbo shouldn't live 100K+. I've seen them with very low miles and destroyed and very high miles and still OK as far as the bearings go-just the seals have given up. Critical is the balance of the unit as well as making sure that the oil gets there.
Second-VF52 is exactly the same turbo as VF39 which is exactly the same turbo as VF43 which is exactly the same turbo as VF48. They all utilize the exact same CHRA with exactly the same turbine and compressor wheel and it has a 9mm shaft with 13.645 OD x 8mm wide journal bearings. The piston ring end seal on the turbine end is identical to the VF40/46 while the compressor end is slightly larger in diameter. These are the same material and the same configuration and have the same issues-give it oil and it will last. This IHI series of turbos has a bit more lag than the VF40/46 due to the larger turbine which weighs more and is a bit more restrictive at lower rpms causing it to spool a bit slower but when it comes on, it does produce a larger volume of air due to the size and configuration HOWEVER, based on the lean and cylinder knock/ringland issues that the EJ25 engines have, I would most definitely go to at least a larger injector and tune it down rather than try to tune up the stock injectors. You'll be working the stock fuel system at it's limit to make it truly effective.
Third-Td04 Mitsubishi turbos have an almost identical configuration to the IHI VF40/46 in shaft size, journal bearing size, and length with one major difference and that is that the design for the turbine shaft seal cup in the CHRA bearing support housing is far more robust and the compressor end design is a bit more efficient as well. This doesn't make them any more immune to failure as I've seen these things so destroyed that even the studs in the exhaust housing were no good and the wastegate actuators are pretty crappy on these too. I would never be afraid to put one on my own car though as these are a pretty damn good little turbo.
Fourth-Td05/06 have almost the same dimensional internals as the IHI VF39/43/48/52 with a 9mm shaft, a bit thicker journal bearings (15.615 OD x 9.3mm wide) but these also fail as easily as anything else when it comes to oil starvation-call one of the companies that sells these in the 16G-20G varieties and ask them how quickly they blow up with no oil. I've had several that the journal bearings were actually broken in half when I disassembled them and they came out in two pieces and I've never seen that in an IHI so sometimes, thicker isn't necessarily better. The one thing that is substantially different about the Td05/06 is that the turbine is MUCH heavier than the IHI VF39 series turbine, which in turn can make it spool even slower but then really spin on top end. This is why it's the design that is preferred for the bigger wheels because it has the inertia to really push those big wheels and it helps smooth them out at high speeds.
All turbos have issues, even ball bearing units. I've had several IHI ball bearing units apart and they are crap. Garret uses a tiny ball bearing setup that I would be scared to death to use and yet, they live pretty well. The hybrid setup is not what I would recommend from experience trying that kind of setup on very high speed electric motors as it produces excess heat on the journal bearing while the ball bearing, no matter how good it is, still has a tiny bit of radial shake and that can prematurely wear the hot journal bearing. When both ends are ball bearing, the radial shake is virtually eliminated because the bearings self-center in the oil as they spin and this eliminates the movement.
I'm working on a roller bearing design for the VF40/46 first and the reason why is that many people simply don't want to spend the money to do a complete upgrade. Most people want a reliable, quick spooling turbo, that can still retain a bit of gas mileage when not being pushed and still want the fun. Anyone that's ever driven a bone stock LGT with a VF40 on it when everything is working right knows that it's a pretty damn good car-quick and fast and nimble and just plain fun. It's US (looking around the room and seeing my own face in the mirror) that can't leave well enough alone.
When most people look at big turbos, they have to realize that the $2000 turbo isn't the only expense. Everyone says they want an 18G or 20G and just think that they can buy it, bolt it on, and go. It then comes down to how much money do you have, how much time do you have, how much expertise do you have, how much patience do you have, and how much of all of that combined do you have.
It takes a lot of money to produce big horsepower-been that way ever since there has been cars. It's not simple and it's always at risk to take something that's designed to live in a certain realm and take it out of that comfort zone, especially if you decide that you want to do it with 100K already on the clock.
These engines are excellent and reliable and solid IF they are treated correctly AND the turbos are the same thing. That doesn't mean that they can't fail. Tires, brakes, exhaust, bulbs, even the radiators all go bad and they are changed and usually to more expensive alternatives and no questions asked as to why they failed. Alternators fail and we think nothing about changing it. Battery won't start anymore and we just replace it. Power steering pumps fail and we just buy another one and put it on. A/C compressors-boom-another one is installed, BUT (jaws music inserted here and LOUD) when the turbo goes, it has the potential to take everything else along with it.
The maintenance is the key, the diligence to check the oil every fill up or every other fill up, regardless of whether it's storming outside or sunny. OCI must be kept up and fluids must be maintained. WOT for 5 minutes at a time just isn't healthy on something that has exhaust flowing through it at that volume and speed.
I'm off my soapbox with one more thing to say and it's been said and said and said in these forums-these cars are NOT for the faint of heart and the faint of wallet. Usually when they are purchased used, they have been beat on, as all of ours have, and there is a reason that the car is being sold or traded in, so there is NO surprise when someone says "I just bought this and drove it for a week and the turbo blew up" or " the dealership said they put a new engine in it" and WHY did they put a new engine in it? Because someone else blew it up.
Buy one of these and expect to love it and hate it all at once. Learn to work on it, save your money, but in the long run, it will give you more smiles than anything else you could ever find in the price range. The AWD rulz, and the handling is better than any other sedan it's size stock for stock, and the engine produces more horsepower for it's size in it's stock configuration than anything else in the category.
Enjoy these cars.