Got my new TFB420 in the mail yesterday I'm mostly playing thru and Eden Navigator/QSC-PLX1602 right now. I also have a bbe-bmax in that rack, and a tuner. Kinda heavy! I typically play mostly upright anymore, but do have jobs where I play both. The Eden Nav/QSC combo does both admirably well for me, and if I need to "a stronger" electric tone, the bbe brings it in spades. While some DB guys will scoff at the eden navigator, I like it quite well for DB-it provides big, round,full warm tones, and has a broad eq section which helps dial in a room, or dial out bad tones/feedback issues. Perhaps I'm not someone who prefers "sterile hifi" as his sound...I've not had a chance to play with something like an I-amp 800 that would fill that ticket. I think that the I-amp might lose some ground to other warmer setups for electric...For me, the Eden Nav doubles real well. The Thunderfunk's eq section is dang near the same, and as such I'm on friendly and familiar terms with it. The 420's timbre and enhance functions seem, intially, to provide much greater response than similarly laid out eden or similar swr's. I played it thru a Schroeder 410, Henry 8x8, and Avatar 112 in the shop last night, and I'm quite pleased with the results. Initially, I think the TFB420 easily hangs with the Eden Navigator in terms of ease of use: It sounds great for electric set flat. Similarly to the Eden, dial out some mids at about 750khz, and it's a nice upright tone... While it may not provide quite the overall volume and headroom of the 1600 watt QSC/PLX, I think it will be quite adequate in terms of volume. I'm curious to see what the "tube emulator off" switch on the new TFB550 does. For some of the guys who want a more sterile sound, this might make the TFB550 the cat's meow. However, I did not find the TFB420 overly warm, and not at all crunchy. It's certain miles and miles cleaner than either the Mesa 400+ or 1965 Fender Bassman I had at hand. More after a few jobs with it, but for now, I'm quite pleased.