I run the AC Pro's w/heel guards and love it.....I was running stock nerfs, with no heels. I came off a VERY short jump and I landed with my toes on the peg, and my heel too far back. My foot went down, and my toes touched my shin. I broke my foot and hyper extended my ankle. It sucked. I got full ac nerfs that week of.
The AC Pro pegs mount to the back of the frame using a side support. It is makes room for a kick starts. It replaces the pegs with extra wide IMS style pegs as well. Takes all of 20 min to put in. The front bolt up to the motor mount holes. You take out the stock bolt, run a longer bolt all the way thru the frame, and then lock it down with a nut. So it is solid. Some tap the other side of the frame with threads, but this is just more work and not as strong.
IMO, they are a must for trail or mx use.
Pros: Safer than nothing at all, cheaper than Dr bills, pays for itself after your first ER visit.
Cons: Acts like a shovel in the mud (I have heard newer styles are not as bad the old style. The new ones use nets in the back)..see my sig.....Like any nerf, it can get in the way of normal work on the bike. Builds a false sense of jumping ability...LOL....you will still bust your ass if you don't know how to work your footing right. A new pair of shoes don't make you run faster.