I actually have 2 Magpul stocks and installed them both myself. As everyone has said, it is more difficult to install than the standard telescoping stock but with a little time and patience, it can be done at home.
Like Curt, I had to sand the thinnest shim supplied with the kit in order to make the stock work with my Bushmaster lower. My advice here is to go slow. I ended up going too thin on one of the shims and was thankful to have 2 others as backup. On my second stock, I sanded down one of the shims perfectly only to find out that the shim was too small to fit properly. No biggie, got back ups.
My next problem was that now the shim is so thin that the buffer tube protuded out too far and the upper receiver wouldn't close properly. The Magpul instructions warn you that this can happen and they state that the threads on the buffer tube are set back a bit to allow you to "Grind" the end of the buffer tube down a bit. I did this with some 100 grit sanding paper and a sanding block using circular motions and after some trial and error, it worked fine and I had a really nice fit between the buffer tube and the rear of the upper receiver. I refinished the end of the buffer tube with alum-black and you can't even tell it's been ground down.
After that, my installs were pretty straight forward. No further "modifications" were required.
So in the end, the MSS M93 stock install can be done at home even by a klutz like me but remember to take your time and follow the step by step instructions. The results are worth it. Great stocks.