Using a Voc Harmonizer in a live setting is a ART FORM in itself. Its tricky and you have to be very aware of what your doing if you want to make it sound authentic.On top of that your playing your instrument also at the same time. Knowing when to use it and how. I have seen acts with the most Horendous use of a harmonizer you can imagine. Use it right it will be a huge benefit to your act..... but use it wrong and you will make a fool out of yourself and to your audience.

I initially used the built in harmonizer on the X1. But, I felt that the vocal parts were lost in the mix - I had trouble getting the balance right between the voice and the auto accompaniment so I eventually bought a VoicePrism. However, I expect it may have been my ignorance in adjusting the X1, rather than the harmonizer.

I have used the Helicon VoicePrism since it came out, but am still not sure the extra harmonies and realism were worth the cost.
($1000 back then)

I am different from you in that I have been complemented on my voice, but never on my accordion playing. However, a little reverb does wonders for any voice.

I suggest starting with the built in harmonizer.

Good luck!