I've been testing and abusing them since 2013/2014 when Bruce first mentioned them to me. I called BS on the claims and immediately began purposely punishing the battery. After many months of extreme abuse I reported back to Bruce that the capacity was still 100%.. Without a defined baseline for comparison, against other brand new AGM batteries, a testing protocol was designed, to mimic real world use, and then other AGM's were run through the identical PSOC testing protocol.
As well as testing them for PSOC cycling abuse (PSOC cycling is when the battery is used for many deficit cycles between 100% full recharges eg; 20% SOC to 85% SOC repeatedly), and installing them on customers boats, none of the Firefly batteries I've installed have yet to lose any quantifiable Ah capacity (I am testing them once yearly).
That said they company is small and the owner (the guy who bought the patent from Caterpillar) is doing more to hurt the company than grow it.. In nearly 6 years he's done absolutely nothing he had promised, in regards to beefing up production to satisfy supply needs.
Supply has always been the biggest challenge with Firefly. Early on there were a few bad valves and the occasional leaking post, quality control issues, but those issues seem to be behind them now.
Also if you do not use these batteries down to 80% DOD you're not using them as designed or getting what you've paid for. I see too many boaters buy them then stick with 50% DOD as the bottom. Big waste of money to do this.
If you can find them in-stock you won't be disappointed.
I would suggest by starting with:
Practical Sailor May 2015 PSOC Testing AGM Batteries
Practical Sailor August 2015 PSOC Testing AGM Batteries