Well I have the Hyperdyne, Rom FX, Voice core and a couple of others and in my opinion the Rom FX gives the best no feedback sound nice , loud and clear, followed by the Voice core from Plecter labs which is another good unit. IMO the Hyperdyne is tricky to eliminate feedback and a little tricky to program. At least the one I have is which is the earlier model, they may have fixed that by now.
So if you can afford it go with the Rom FX it rocks!