The Duncan Powerstage is a class D poweramp, totally flat response. Basically it's a solid state poweramp.
Word is the build quality is solid and it's a very good, loud, clean poweramp. Also the onboard EQ is very powerful and sounds good.
Like any solid state amp, it doesn't follow the impedance curve of the cab it's plugged into so if you're using a rack preamp or pedal for your tones, it's not going to sound as good as a tube poweramp. But you can't beat the Powerstage if you're using a modeler or reamping a tube head with a reactive load, where an impedance curve has already been applied to the signal.
Personally I'm waiting on Duncan to make a stereo rack Powerstage like the 700 but with the new EQ controls of the 200. They haven't released any info that anything like that is coming but it would make sense to update their flagship Powerstage 700 by applying their already-developed EQ tech of the newer 200 model, so it follows logic that such a product might be released at some point. That would be perfect for me and my setup and I'd buy it on day 1 if they ever release it.