Hi dear7,
I don't know anything about Tc helicon, but I'm using Digit V2, so I think I can share some ideas with you.
Digit. V2 has basic functions like Compressor, Reverb, Enhance, Harmony mix, and each of those functions also has 3 mini functions to play around with. Able to use with Condenser mic or Dynamic mic too,
I'm using it because I no longer want to be in any band or with any other (too lazy to practice with others). I'm now a "One man band" type so I will occasionally need some fake harmony to avoid monotony or even boring for the audience.
So far I'm happy with it, but of course nothing will replace the real human voice.
Here's my sample that you may have more idea if you want to watch it;
[A friendship needs a little mulch of contacts every so often-just to save it from drying out completely.
I always have great pleasure being alone by myself to play, If you're playing for any other reason, it won't last. http://youtu.be/_tkGVGOKQ8c