Silting is primarily a function of diving technique -- a combination of trim and kick, and where you are with respect to the bottom. I do not believe it is possible to do a full-leg flutter kick and not send water downward; the physics just require it. If you dive far enough off the bottom, in a horizontal position, and the kick is not too big, you won't do a lot of silting. But I think you can do a frog kick and not disturb the bottom at all, where a flutter kick giving equivalent propulsion will.
Frog kicking is really more comfortable and more efficient in a stiff fin. Even very flexible blade fins don't work very well.
Flutter kicking in stiff blade fins, for me, is extremely uncomfortable. But since it's the kick I use least, that's not an issue.
BTW, I have owned and used both, as a novice diver and now, a bit further on. I much prefer the blades. All the kicks I know, I can do in both, but they are easier and more efficient in blade fins, except for the flutter kick.