As an OB-6 owner I was contemplating replacing it with this one, or even potentially keeping both. I had heard so many people gushing about how amazing it sounds, and how much better it is than the OB-6 (similar to the P5 Rev 4 vs. P6 which I agree does sound better).
So I powered on expecting to be blown away, but I wasn't. In fact I found this synth to be extremely boring. My Pro-800 can make strings that are more lush, and the OB-6 can do almost every sound I heard on this but much more! I returned the module as I could not justify the expense and believe I'd be better served by adding a P5/10 Rev 4 to my setup.
If you are considering this one, you've really got to love the old OB-Xa sound (I did not find such a strong difference between the OB-X, Xa, and 8 filters other than the Xa being overall brighter). I guess I prefer the OB-6's more unique SEM-based sound and marriage between Prophet and OB components.
I will say it's a good-looking module and extremely well made. It's a bit longer than I imagined so you'll need a wide desk, but the sound was just not for me.