The reviews on the GR27 AGM models are mostly good, but in the description, they state they're "hybrid" technology, designed for storage and starting. Sometimes hybrid batteries aren't quite as robust as true deep cycle batteries, and they may wear out faster depending on your usage. The warranty is 12 months replace, 13-36 months prorate, so that's not too bad.
Just looked at some of the other ones, and they have rated their amp hours @10 hours, so be careful of what the posted amp hours will be. 20 amp hour rate (half?) is what most sellers use.