Gel or AGM batteries reduce the need for periodic water checks, but otherwise are no better than quality flooded cells deep cycles.
The Exide Xtra is a golf cart type deep cycle, similar to other GC2 size 6v's. The 135 is a pretty much a standard capacity for this type, 226 AH (230 is the norm). It is also available in the slightly higher capacity (240 AH) GC-145 model. Compare prices with other 6v GC2 (golf cart) batteries with the same AH or RC rating. Sams' Club & Costco offer some good value in their private label GC2 batteries. If you have golf cart stores in your area, heck them for pricing too. Some discount, others may not.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL