The ribbon cable thing is really nothing. I've been gigging with my Carvin for years and no problems. If there is, open the head, spray some Deoxit on the cable connection, and your done.
The Markbass heads are great and so is the Carvin. Some say the Carvin doesn't do thick and warm but that's not my experience. It does it but it takes some odd adjustments, compared to more traditional amps, to get there. That being said the Markbass has a great sound and it's easy to dial in modern-to-old school rather quickly using their filter knobs.
The Carvin is cheap and can be returned within a 10 day period so my recommendation is to buy one, compare it to the Markbass, and pick the one you like. I'm a Carvin fanboy but I really like Markbass and GK. Competition in a free market is good for consumers because it makes the manufacturers try harder.