I have the one sold by sksman (made by buffer technologies). I was a bit disappointed that I had to trim it down before it would fit in the back of the dust cover. Then the hole for the spring was way too small, so I also trimmed out the thin wall part of the spring hole. Seems to work ok now.
Doesn't cause jams, and I like the fact that there is no more metal on metal shock, although shooting sks's with and without it side by side is kind of hard to notice much difference. Did that today, actually.
However, I have read that the preferred one for sks's is sold by blackjack buffers. So, if there is a next time, I'll try one of those.
Goes for about $11.