I have a first model Sunn model T. This one is the king of Sunn amps in most people's minds. It is loud, and has never had a reliability issue. As far as tone, this amp is both huge and clean sounding as it was designed for both electric bass, and electric guitar. The 6550 tubes are not known for sizzling distortion or breakup. It probably best to decsribe this as a high powered Fender Bassman. It is simple, like a big block muscle car, and needs room to run.
It is so clean, you will need a pedal in front. On the positive side, there is so much bottom end ass, it is a revelation to behold. You may find that all (well maybe not all) amps you have ever played now sound thin and somehow unsatisfyingly cheap on the bottom end. I have seen guys wheel their flashy gear next to mine when, and seen their faces look hurt and sad after a few chords though this thick, natural monster. I had a 4x12 cab at the time.
I'm never gonna sell mine. Surprisingly, I'm not sure I would recommend one. There has been so much gear created that is more versatile.
Good Luck!