I've had better luck with the fretless emulator on the Zoom B3/MS60B than I've had with anything else I've tried (in that price range).
Setup of the effect parameters is tricky and touchy. Depending on context, I've gotten exactly that "mmmmwaaahhh" sound described by @GMC.
I'll also add that pickup selection and finger playing technique do matter to get the best emulation.
IMHO, the fretless emulation is a real crap shoot, and a dozen different people will probably have a dozen different opinions about how good it works or not.
I think its pretty OK for the flavor, but just don't expect too much from the effect under real close scrutiny.