I'm running a crimestopper sv-9154 mirror that's pretty good for the money, along with a crimestopper backup camera.
Wiring is pretty simple. I did this a few years ago, so I forget exactly what I did step by step. I supplied power to the mirror using the subaru homelink mirror power plug, which you can find if you remove the map lights. I forgot where I grounded the mirror, I think somewhere near the glove box.
After that, you run the video cable and reverse cable to the back of the car, connect the video cable to the camera, tap the reverse cable to a reverse light bulb's power, and that's it for the mirror part.
For the camera, you connect the video cable to the mirror video cable, ground wire to a ground, and I think I also tapped the reverse lights power for the backup camera power as well, using the same vampire tap for the rear view mirror reverse switch.
I've never seen the outback's setup, but here are some thoughts on mine.
-The 3.5" video is pretty small. I knew it was going to be small, but it was a little smaller than I had hoped it would be. There are bigger options, but I didn't want some big rear view mirror hanging off my windshield.
-The backup camera display actually gets in the way sometimes. Since the video takes up about 1/3 of the mirror, it really gets in the way sometimes, almost making things a little more dangerous. You do have the backup camera video to help you see, but like I said the small video size can make it kinda hard to see things.
Sometimes I regret doing it, but other times I don't because it is helpful under certain conditions. For example, if I had two big SUV's or pickup trucks parked next to me and I'm trying to back up, it helps me see whats coming since my camera has a wide field of view. One of the other reasons I got it is because the legacy lacks a rear wiper. Sometimes in the winter even after I clear my rear windshield, it gets covered with snow again quickly. So it's nice to have the camera for when the rear windshield is covered with snow.