HUDs are mostly useful for fish and nit spotting. There isn't a huge amount that you can infer if someone has stats like 14/8/2 as opposed to 17/7/2.1. For that you need your table reads and your awareness of the hand.
What the HUD does for me is spot the guys who are playing 80% of the hands, but never raising, or the guy who has played 2 of the last 100 hands and just raised UTG.
It is not a substitute for reads, but it helps with identifying raise ranges etc.