The catch with the Poly Evolver Keyboard is that you can get attached to its specific wave shapes. I've adopted these as the overall sound that I want to have, and it's hard to imagine composing or improvising without them. Granted, many are musically unusable, but a substantial number are quite beautiful when tastefully set.
Having recently spent some quality time with a Prophet 12, I can finally say with certainty that it's a superb synthesizer. It's right up there with the other instruments in the DSI line up. But it has also shown me all the more what an exceptional synthesizer is the PEK. The good old Evolver is totally unique, a bit unpredictable, and for a partly digital instrument, has an unpolished rawness that has a musical charm that's hard to put aside. And that's a key difference between the two instruments: whereas the Poly Evolver has a rawness that hints at earlier digital instruments, the P12 is the ultimate in polished and refined synthesis. In a sense, it's perfect. But I don't think I could blindly recognize the voice of a P12, whereas I can recognize the voice of an Evolver in a second.