Just to add even more variety to the collection of reviews this amp is gathering I thought I'd add my two cents...
First off I'm playing a Fender Jaguar into the MiBass 550 and that into a lovely Midget T. As far as I'm concerned the sound is the best I've ever got. It's not even comparable to the majority of set ups I've used; the MiBass also beats the MAG 600 (the MAG series being, in my opinion, brilliant when you get one that works as it should) which I was going to play into the Midget. I made the switch as the MAG 600 came with added fault and, through some kind of miracle, I found a new MiBass 550 for merely £330 and thought that it would be worth a try. I must agree that the VU is too small, and also add that the controls can be (although they are well weighted) a little close together; however, it has all the versatility most bassist ever seem to need and an excellent range of outputs on the back (the DI output is in my opinion a must!). To be blunt, this amp is summed up by two statements:
1) It looks a little silly (although I'm sure some love the look)
2) It drops almost all weight without compromising amazing tone and volume (it can even do earthshaking through my Midget!)
The tone and power behind this amp really is brilliant; through the Midget T the MiBass delivers proper, full on, punchy bass and also a superb high end. The amp also stands out very well in a mix and, in my only test so far with it in a band situation, delivers all the volume needed for any gig without a PA.
This is the lightweight amp Ashdown always should have made and what's more, it punches well above it's weight. If your considering it, or even just curious, my advice would be to try one and just see it in action.
I can finally carry my gear to a gig on my own without a car and still deliver like I've got my old 4x10 behind me!