I've demo'd this amp at a local guitar store. Unfortunately, all of the clips from that day (Dual Recto, 5150 III, Twin Jet, Mark V,etc.) were never used since the shop owner and workers were fairly new to mic'ing the amps.
For starters, I've only played through two Bogners - the Twin Jet, and the Ecstasy. The Twin Jet is pretty cool - much more my speed than the ecstasy. It did an early Van Halen tone really well, and handled metal well.
It was a very open sounding amp - surprisingly very little compression for the amount of gain that was going on. Probably the least compressed tone I've ever gotten for metal. It worked incredibly well for Opeth type riffs - lots of open chords and dynamics going on.
My biggest gripe with the Twin Jet was the bass response. For me personally, I like a pretty quick response and a very tight feel. Typically, that means rolling the bass back a bit more than most. When I did that, the sound thinned out a bit, and still retained a moderately woofy tone. Long story short, it wasn't great for a thrashier type vibe. The amp
did have a tight feel, it was just a little overbearing on the low end, or too thin when I got the uber lows out.
I'm not sure about the clean capabilities. The shop I was demoing for is trying to appeal to metal players more and more, so we never really messed with dialing that in. I will say though, if you're used to running a single channel amp (relying on the volume and tone pots a lot), it cleaned up VERY well due to it's lack of compression.
I thought it was a VERY unique amp, and I can totally see why a fan of the 6505 wouldn't really like it. It's open, airy, and has shit tons of gain. And as I remember, it was running KT77's for OBSCENE amounts of volume.
Let me know if you have any more questions, I'll do my best to help out
