First ski was a 1976 JS440 (awful POS) and then moved to a FX1, the FX was more stable plus it had a lot more (double?) power of the JS, I thought I could never want for more. When I rode a Superjet, I thought they were too wide, too stable vs. my FX. I also have a FX hull that has a ton of mods done to it (pump and intake from SJ, shortened, tubbies, pole bracket moved forward, lowered gunwales etc) that I rode for a season.
I've since moved on to a RN, and now a Backie Chan.
I haven't had the chance recently to ride a stock FX, or one thats stock plus the 144 pump mod. There is a local rider who has a FX thats shortened quite a bit, and I can't express how much I dislike riding it. Is it because I haven't been on a FX in awhile or is it because of the mods? Who knows...
They are fun... In my experience the bond line could be lower, or wider to help a little with stability.
Also, the FX vs. _____ debate is never ending. There are a large group of people who absolutely swear by the FX1, and conversely there are those who can't stand them.
Heres the bottom line IMO, If you love your SXR and hate a 550, than you'll probably dislike the FX1. But, as mentioned above everyone can learn to ride something well.