I have some Hapstone Opti clamps and they do work well on many FFG knives, but I personally still prefer the Hapstone Universal angled clamps primarily; with a close second choice the Hapstone Lite clamps.
If you were to get yourself a Hapstone Opti system with an extra set of either one of the above clamps, you would have a very good system.
The Opti clamps have an angled cutout to assist in clamping FFG knives (like many Spyderco grinds), but of course that is very specific to an exact angle of knife grind. They make up for variable grinds by being very thin, so the front of the clamps can flex when tightening and end up conforming with the grind a bit more. Because they are so thin and flexible, they can not clamp a knife as secure as a more "beefy" clamp. They are secure enough, but personally I prefer a rock solid clamp.