I've shot a Rad 2 nearly ten years. I like it and wouldn't be afraid of a used one but there at least two issues to consider.
1. The aluminum plate that attaches to the butt stock would have been fitted to the original gun. Depending on how much material was removed, you may or may not be able to fit it to the butt stock of your gun. I don't know if that plate can be easily replaced or not and if so, at what price.
2. The Rad LOP adjustment is IMHO their worst design feature. If you're not familiar, steel set screws are tightened into dimpled depressions in an aluminum block. If the set screws are over tightened or under tightened, it can cause significant damage to the block. Several years ago I looked at a used Rad so damaged I wouldn't have taken it for free.
I wouldn't be afraid of a used Rad in good condition. Just be sure it is in good condion.