A couple of years ago I did a weightshift conversion after a few thousand hours and many years of 3-axis experience in a range of types. I had no problems at all in the air but the really hard part was directional control on the ground. I also found learning to land harder than I'd expected - not the control direction, but judgement and avoiding accidental roll inputs (maybe it was a personal biomechanical issue). My plan had been to add weightshift instructing to my repertoire but on reflection decided that it wasn't sensible without a lot of experience - the published minima seem very low. YMMV, as they say.
(To put this into perspective, a few years earlier I solo-ed in an R22 in record time and expected weightshift to be similarly easy)
I know several people that fly both but I think most came from weightshift to 3-axis.
HFD