Yes, I am still a fan of Firefly batteries, but a caveat or two is worth mentioning. Like any relationship, there has been a bump or two in the road.
Twice we have had a battery develop an internal short. The first time we discovered it quickly, and it was immediately replaced by Firefly. The second time, our monitoring system wasn't good enough to catch the issue, and we developed a chronic imbalance where half the bank was overcharged, and the rest undercharged. By the time the issue was apparent, permanent damage was done to all the batteries. Firefly stepped up an replaced the whole bank within the terms of the warrantee--keeping us happy.
We learned. It is quite likely that if we had seen the issue early on a minor change in charging procedure might have alleviated the issue, but we'll never know for sure. We have since significantly upgraded our electrical system monitoring system, and a minor imbalance is not going to sneak up on us again.
As for running A/C from the batteries, sure it's possible. One of our A/C units draws about 850 watts when running. That's about 4 times our normal house load. That is easily supplied by our 8 battery bank and 3kW inverter. In the absence of any solar power, we'd need to run the generator twice a day for 3 hours instead of once a day for 90 minutes. It is important to remember that it doesn't matter what kind of batteries you have or the size of the bank. Batteries do not make power they just store it. A bigger bank means you can reduce the number of times you start the generator, but your total run time will be about the same.
All that said, in 5 years of full time cruising we have run the A/C units while away from shore power exactly once, so it was not a priority in our design decisions. If your plan is to run A/C units regularly off the grid, a larger system than we have might be needed.
Fort Lauderdale, FL, USA