I'm favoring the Rocktron as of now from the reviews and the easier set up I've read about. I can't sing very well, will this effect my ability to use one?
You don't have to actually talk into a talk box. You only put your mouth over the tube and shape your mouth to make the sounds you want. It takes some practice especially to get words clear but it's a cool effect if you can. I've got the Heil but I haven't tried any others so I can't comment on them.
I like the Rocktron model myself. You don't sing when you use a talk box, there's a small driver at the base of the tube and it sends the sound through the tube. You shape the tone with your mouth and your mic picks up the sound.