I use RaceRamps RR-56 and I feel that they are very safe. I have never had any issues with traction or slipping on the garage floor, and they have a built in wheel stop to avoid the previously mentioned launch through the garage wall. Pricey too, but I got mine locally on Craigslist from a Porsche club guy that won them at a Track Day event and never used them. He just wanted to get them out of his garage, so I snapped them up for a steal, in the original box and not an ounce of dust on them.
Honestly, if I had to pay full price, I never would have bought them.
^^This one comes with a free Race Mat. If you can do it, shoot them an offer, see what they say.