Other than some sort of fault, either with the manufacturing of the battery(s) or with your charging equipment, the main reason for a battery failure as soon as 2 years is "murder by the owner". In other words how you use. AGM batteries are even a bit more "fussy" in how they are operated (and cared for) than flooded lead acid. With few exceptions, batteries do not tolerate very deep discharges (below 50% charge) and/or being regularly used without being returned to a full charge of 100%. To achieve a 100% charge, it usually takes at least 6 hours of continuous charge time for a properly operating, properly setup charger (or alternator), sized for your bank. Unless you boat dock to dock (with shore power used almost every night), or have solar panels, you are probably not achieving 100% charges (often enough) even with long engine runs. Stock alternators do a poor job of recharging deep cycle house banks.
So, think carefully about how you have been using your batteries. If you were "treating them right" and you still had this 2 year experience, then check out your equipment for issues. If it turns out to be the way you were using the batteries, then 2 choices. Buy the cheapest deep cycle golf cart flooded lead acid batteries you can find, and consider them basically "disposable" (replace every 2-3 years) or make changes to the way you recharge your batteries (a true 100% at least every few days) to obtain a more "optimum" life expectancy.
Edit: Sorry, to your original question, I don't know those batteries, but I concur with buying a known brand with an easy warranty experience. If you go the inexpensive route, check out Costco or Sam's Club (for example)
