I really think the answer to this question is that it's mostly player dependent. I have used and love PT4 however it isn't available for every site I play on. I've had very good results on BetOnline
this year where PT4 isn't available, but that doesn't mean that it's because I don't use a HUD. It's more likely that BOL has a fairly weak player pool and my skill as a player has improved slightly.
My personal opinion regarding HUDs is that I shouldn't expect it to make my decisions for me. What it does is provide me with very organized information with which to make my own decisions. There's a significant difference there, folks...
Where I think many of us have fallen short is using PT4 to learn about our own play outside of our sessions. Analyzing our own player data to determine our leaks, our weaknesses, and to underscore what we're doing right is more important - IMHO - than the HUD during play. This is where I miss PT4 with my play at BOL. I'd love to see how I'm doing statistically even though my results suggest I'm doing well. (Most likely, there's a LOT I could do better!)
So, I'd suggest that whether or not you want to use a HUD, the software will be quite instructive as to your play and for that reason is a real benefit for any player.