I have tested it, while doing a 2 Finger FR it doesn't do anything since I have them timed very well. One goes up, one goes down etc.
While doing a 3 Finger FR you will see a little impact, it depends on your timing that you had before, I for example can time my 3 Finger FR pretty good cause I play guitar, but not perfect since I preferred 2 Finger FR in W:A for years now. Well and 4 Finger FR you will notice it a lot. I couldn't try 5 Finger cause well... ctrl, windows, alt and then spacebar is workable. Can't quite reach alt gr though. xD
If it's cheat or not?! I don't know, it removes the technical delay which is removed in other games anyway. W:A is an old game and things like this are pretty normal in current games that you can perform the same action even if you have still a certain key pressed down mapped with the same action. (3D Ego Shooter, MMORPG, 3D Strategy games etc)
If it would be patched into W:A by Cybershadow it would probably be awesome, remember it's not like you press space and get 2 or 3 space bar presses out of it. Every press is done by the human, nothing is multiplied by any external program. It's just more accurate. I had a long discussion with DarK about this already (who showed me this) and it's probably more of a morale decision than an actual definition of cheating.