I've used HUDs off and on since they've come out.
#1 - I've been playing poker since I was a kid, and have seen literally millions of hands. As for starting hand selection there's nothing a hud can do for me.
#2 -
odds and outs are made MUCH easier with a hud, but if you rely on the hud 100% you will miss it live and possibly get lazy ( but it can also become a decent learning tool ).
#3 - A HUD with decent features makes note taking much easier. For the first decade of
online poker I didn't use the "player note" feature with most sites. I relied on trusty old notebooks and a pen to track regulars.
#4 - If you can't beat micro rings and sng's you should probably solidify your basic fundamentals before you worry too much about a HUD. A hud will help you plug leaks only if you understand why the problem is a leak.
For example if you're forced to fold a mediocre starting hand regularly because the button constantly reraises you a hud will show you percentages that tell you to tighten up middle and early hand selection but it wont really help you understand fully the necessity of positional play or better yet that the guy stealing your calls and min bets knows damn well that position means little or nothing too you.
So I guess I'd say a HUD is in no way cheating. I calculate odds naturally. Those I don't, I've memorized. Those abilities aren't natural for everybody.
Also, a HUD is only going to improve your ability in great manner when you have solid fundamentals, and discipline.