Well, okay, what more can I reveal....
The FR was on a MIM Strat (HSS). The pickups on that thing were garbage. I bought the thing intending to upgrade the pickup, and got the FR model because I figured it would have more bells and whistles than the normal trem. The other reason I dislike that guitar is the neck. On the other hand, every time I try an AmerDeluxe, the neck is like sweet buttah.... The neck is always the one thing that'll make or break a guitar for me, above all else.
The FR stayed in tune pretty good, actually. The downsides I perceived were that it was a massive pain to set up, and that it sucked the tone and sustain outta the guitar. I would have preferred tuning problems to the amount of tone/sustain I perceived that it diminished.
I put big huge .013-.056 strings on it and had to detune to C# so the thing wouldn't buck up. I kept intending to add two more springs but never got around to it. I know SRV had that gauge on his Strat and he tuned flat to make it easier on his left hand. If I get the nicer Strat I'd do the same and make sure to beef up the springs first thing. I prefer fat gauges... I've currently got 12s on this 60s era off-brand Japanese-made surf guitar someone gave me.
I thought Vai and Satriani used the Ibanez trems? I wouldn't know.
I plan on one day installing a Kahler on a guitar. By all accounts it is very much the superior machine.
The guitar I use now has equally cheap electronics (though cheap by 60s standards), and the slab (I think it's mahogany, I'm not sure) and neck are much thinner and flimsier than on the Strat. But it's a hardtail (primitive design), and when I run it through the same settings, it sounds far, far better to me.