Short version- My main rig is an MB500 through 2 Neo 112s stacked vertically and I think it's great.
Longer version- I was always skeptical of 12 inch speakers for bass. When I was growing up, 12s were either guitar speakers, or in the step up practice amp that still sucked. For years, I gigged a 410/115 combination. But as I've hit middle age, I decided I wanted less crap to move around, and started trying out 112 cabs, and was just blown away. Punchy, with plenty of low end and a nice high end snap. They also make a shocking amount of volume. and I can carry them with one hand. I ended up with the GKs as a sort of price/performance trade off. They really hit the sweet spot for me. Bergantino's are a little nicer sounding (can't put my finger on it) but just shy of twice the price.
There is alot of subjectivity on tone. The Neo 112s are definitely in the modern camp with kind of tight lows and a lot of sparkle in the highs. While that is pretty much my sound, I find that I like them with the tweeter attenuated a little bit. I think if you already have and like GK gear, you'd really like these (whereas if you were looking for more of an ampeg sound, they'd be a pretty bad choice). I think each is rated at 350 watts, and your MB500 is only putting out about that at 8ohms, so you should be safe (you could also run a large amp, just don't dime the thing). I am using 2 cabs because I think they are a little fuller sounding, but one was still plenty loud, and would be more than enough for any scenario where you have FOH support.