We have a cabin by Fast. My father-in-law did some testing for them and has the M-10 on a 96 vmax xt 600 and a 97 srx triple.
I've been on both sleds and was impressed with the suspension to a point. The older sled (96) handled much better than stock, the 97 triple wasn't as noticable IMO. I also own a 97 vmax xt 600 and the suspension on that was just fine for my riding. I'd consider putting that on my 96 sled as that one doesn't really have as good as suspension as my 97 (if the price came down some more).
Last weekend we went through some hideous trails, extremely bumpy. My father-in-laws sled was just as bumped around as ours was. In fact, I think he complained the most of all of us at the end of the day. =)
Personally, I can't justify the $$'s for the upgrade when I feel mine is just fine.