The Polly's hella lo-fi and gnarly, but endearingly so. Watch the levels, because it overloads and distorts at relatively quiet osc mix volumes. As a MIDI sequencer, it's not very good - it doesn't send velocity out, and busy sequences actually mess up the internal and external timing. BPM is saved per patch, which can be frustrating when the Polly is the master clock.
As a self-contained unit, slaved to an external clock and humming along in its own world, the Polymorph's a fabulous, distinctive instrument. The sequencer's powerful, but a doddle to use. The dodgy sound cuts right through a mix and is excellent for darker, more electroid numbers. The Mellotron waves are pretty sweet, and its multitimbral options are rather smart.
So, it's not for everyone, but there are damned good reasons people hold onto them. I only sold mine to finance a Sunsyn purchase.