I am the original owner of the lightweight GK MB with the matching extension speaker. Kept inside and a smoke-free home, gigged once. 15" configuration.
Interesting story, I used to live near GK in Stockton, CA. I met Bob Gallien, and he was kind enough to let me play all of the MB cabs one afternoon. They only sell their stuff through dealers; he was not even making a sale, he was just a cool guy. I tried all the various combinations, and I found the 15-in speaker was the best all rounder.
Before this I had very large bass amp stacks, but I don't gig anymore so I got the GK which is lightweight, clean, and wonderful.
It's in perfect shape, comes with the power cords for each of the units and the speaker cable to go from the combo amp into the extension. I also have the original packaging for each of the units (pro tip: never get rid of your original packages for music or stereo equipment!)
You can read about the stack, but basically the combo amp is 200 watts, and the extension speaker is a powered extension at an additional 200 watts. So when you connect them both together you get 400 Watts.
I played an evening show, and we covered Pink Floyd, Dark Side of the Moon. For this gig I used no effects, just my bass plugged straight into the amp and it was perfect for this type of music.
Local sales only, will not split up the units; they're sold as a pair. The price is firm.