I own the Demeter SSC.
I don't know what your expectations are, but it's not totally silent. With a cranked 50 watt amp, it will cut the volume significantly, but your downstairs neighbors will still hear it. 50 watts, significanly quieted, is still pretty loud! Think of it more as a studio tool to provide some isolation rather than a devcice that will let you crank your Marshall without guilt at 1:00am.
There's not a lot of room for mic positioning. About a foot; maybe 18 inches max. Larger mics can be problematic. Tube mics also present a challenge because, stock, there is a panel with only a jack for the speaker cable and another XLR connector. I modified mine. I removed the "arm" and now I just use a small 4 inch tall desktop mic stand with a weighted circular base inside -- it allows for more positioning options. Then again, most people will just use a 57 or 421.
It sounds decent. Not ideal, but I've gotten some good tones. The amp, speaker, mic, pre, guitar, and player obviously have a lot to do with how it sounds and YMMV.
I still use a POD XT sometimes out of convenience, if that says anything.