RE: improvement on the 4 in 1 for falcon 40
that is basically the same as the rudder trim, but with an exanded scale. It controls if the yaw is drifting and you always have to put rudder stick in to hover straight. Check out the venom night ranger Fp manual for more info
also I don't know if the dude that started this ever got it resolved, but yes you can use the blade 4 in 1 in your heli, although I am not sure if it will fix your problem.