I honestly don't hear anything too special there and have gotten better ZZ tones with other gear. I also heard a lot of reliability issues with those, I was even considering them at one time but passed when I started reading into them.
You've heard tones that good from amps priced only $500 retail? I can't say that I have. Interesting comment on the reliability. I knew Ampeg had had some issues of that nature with some of their amps, but have mostly heard good reports on this particular model.