I have flown the Spinblades for two years (actually one set a cheap clone of them), and I can’t really say that I have had any problems with buoyancy in the wind with them. They are an asymmetric airfoil that is better described as semi-symmetric I think.
The Heli-Tech blades with flat bottom are quite popular with the scale builders for two reasons; they make them in CCW configuration, which most full-size heads rotate that direction. And the blade profile is closer to the real thing because real helicopters don’t fly inverted, and it allows slower head rpm so the main rotor sounds more like the real thing on the scale models.
The Rail blades are also not symmetrical. They have a quite interesting airfoil that I’ve never seen anywhere else with washout in the bottom part of it. It has a sort of “cusp” on the trailing edge underneath that washes out to symmetrical on the tips. And the tips have swept back leading edge and tapered trailing edge. They look the same as the RotorTech blades, but they are not the same in the way they fly. The fore and aft CG of the blade is different on the Rails and they are very torsionally rigid, which I believe prevents twisting and more precise “flapback” of the blade in the rotational cycle when cyclic pitch is applied. The result is that they run virtually quiet. I did a double take when I took off with them because there was just motor, geartrain and tail noise. The main rotor is quiet.
The worst ones were the stock Align blades. Very noisy tips, quite flexible blade, fatter airfoil. The Align ones are obviously made for 3D type flight and not efficiency. The fatter airfoil provides more “bite” for rapid maneuvers. But at the expense of power required to turn them. They consumed the most power both in hover and cruise, and have a distinct “slap” noise and more vibration in turns because they flex out of track. The Align blades are made to operate at extreme headspeed so the centrifugal force makes them track. At low headspeed (I was using 1,640 rpm) they are horrible. In the turns the Aligns went so far out of track that the helicopter sounded like a Huey going by. And it is obvious in the logs as well - with the Align blades on it the amps would climb to 27-28 in the turns, drawing 640-650 watts.
All helicopters probably can’t use the same blades due to disc loading, the speeds the heli is flown at, head geometry, etc… But despite all that, the stock Align blades DEFINITELY are not suitable for a UAV heli of any type. At least not if you want decent efficiency and a quiet-running helicopter.
Forgot to mention another problem I had with the Align blades - a distinct tendency to bob the tail up and down in the pitch axis. None of the other blades did that. They would’ve required higher headspeed to settle them down. I left it at 1,640 rpm to try all of them because I didn’t want to skew the results, and just put up with the bobbing. But it was not suitable for UAV stability at that headspeed with those blades.