I confess that I use KOPS, largely because that’s the way I was taught. I’m open to alternatives.
My only (small, all things considered) beef with FIST is the set of initial conditions: this clip-on, this stem, this spacer stack. That is to say, I understand the reasons behind the initial conditions, but I often have to move a bit beyond them. If the customer’s question is, “Which Cervelo should I purchase?” I end up doing a lot of math in an effort to determine which stem/clip-on/spacer stack will yield a workable bike for that customer’s optimum position.
In a road bike fit, I’d think that stack/reach to the bar would be a pretty great set of numbers. I confess that I’ve dragged my x-y tool around the shop, just to see how things might relate.
Color me intrigued.