The damage to the receiver is probably because the receiver is made of aluminum. It is softer than steel obviously, and might scratch or wear down if you are constantly removing it and installing it. At the very least, I can see the annodized finish wearing off where the light clamps on.
I wouldn't let it ruin the gun though. The Sig aluminum frames are good for a lifetime of shooting and can easily hit 100k rounds..in 9mm at least. A little cosmetic "wear" on the light rail isn't going to affect anything.
I had a TLR-2 and regret selling it. It is a top notch product IMO, next to a Surefire X series light that is. The TLR-2 gives you a laser for the same price of the new Surefire X300 which doesn't have a laser. I'm not a huge fan of lasers, so if I had to pay $250 over again for one of the two, I'd go with the Surefire for a more powerful and better shaped light beam.
Crimson Trace makes laser grips for the P220. Other than that, I don't see any other options for mounting a light/laser without using the "tac rails."
