I really liked thee M900 I owned and would still have it if I hadn't decided to switch to in-ears. It's so much more than just a distortion unit with an amp attached.
The 500 watt may interest me even just as a preamp if the price is right, or if I wait for used one.
Have to say I am slightly surprised about the big hooha for such a mediocre release though. Everybody knew about the cabs, so really the amp was all it was about and it's hardly breaking new ground in the market, although I would imagine they'll sell a ton of them!
I think Doug at Darkglass is taking a leaf out of the Apple playboy. Lots of big noises over baby steps in "development", if you can call them that. But people will suck it up and, as with Apple, will pay through the nose for it!