HUD is just a tool which collects statistics about your opponents and displays them. As with any other tool most important is to know how to work with it to get advantage. A tool can be very powerful but if you do not know what to do with it it can cause more harm than good. There are free HUDs on the market like easy poker HUD so try it, try to learn how to use it properly and decide for yourself. If it works for you you can buy better HUD later. If not you can switch back to not using HUD.
Pre Black Friday when I played waaaaay more than now and multi-tabled I used one. But to be honest....I didn't really like it. It distracted me. I focused too much on the numbers and not the situation at hand. That's my fault....I didn't learn to apply those #'s to the situations correctly. Maybe had I done that, I'd have appreciated it more.
Now though...no, I don't and wouldn't. I don't play more than 2 tables any more and I've come to realize that many online players....may not be the same player that those #'s correspond to. Could be a roommate or spouse playing that play completely different to what your HUD represents. That could just be my tin foil hat approach to life though.