Just curious, what didn't you like about the GK combo?
Nothing. Fantastic build quality, super flexible EQ, pre and post switching on the DI, ridiculously compact and very loud for it's size. Once you look at the details, the higher price seems perfectly reasonable compared to the Rumble.
However, there's only two ways a compact amp can go: Slanted towards maximum output/restricted frequency response, or the opposite, an extended, full-range response with relatively low maximum output.
G-K walked a fairly narrow line with the MB110, and with a bit of bass boost, it sounds surprisingly full with a 4-string. The treble response is restricted as well, so that it balances with the tighter low end. Just what most people want and need.
In my case, I was looking for something to use only for very quiet gigs, and only with 5-string basses. Boosting the bass control actually made things worse, because it fattened the E string, making the B string sound weaker in comparison.
I would have been happy to give up a bunch of headroom, if it got me a more extended low end. I actually thought about swapping the driver out, but it turns out that current high-performance 10's won't work in 0.8 cu ft.
I briefly considered making an adapter so I could mount a FaitalPro 8IPR200 in the G-K cab. Duke LeJeune at AudioKinesis was kind enough to help me with porting specs. The result would have been a poor man's version of a powered Arnopol/Greenboy Crazy 8, and it would have sounded awesome.
Unfortunately, 100 watts wouldn't have been enough to drive it the way it deserved, and the cost for the driver alone was going to be well over $200 by the time I imported it.
In the end, I chickened out, and traded down to the Rumble. I may regret it later, but for now, I'm having fun lining the Fender with some polyfill. We'll see where this takes me...