I wouldn't go so far to say "not recommended". It works fine in all the respects you mention, it just tends to scroll very fast compared to how it feels on the Mac native side. If you use a very light, short two finger scroll move it is usable. You just have to get used to it.
Cursor movement is fine, click (tap) sensitivity is fine, it respects the two finger tap as a right click... Pinch/Zoom works in some applications and some not (and that is true on the Mac side as well). The three finger swipe to navigate is one of the newer trackpad software features and doesn't appear to be implemented in Parallels yet, but that's no surprise.
I think the trackpad is implemented fairly well. It could just benefit from some tweaks in Parallels.