I have used one my last couple trips, and like it. These are small batteries, smaller than I would normally carry for a long day in the park, with taking pictures, refreshing for fastpasses, etc. BUT since I can swap them out often, it makes for a lighter bag!
Once you know where the kiosks are, they are easy to use. If I'm going by a kiosk, I usually swap out even if the battery is only partially used, cause, why not?
One thing good to know, is each kiosk has a 1-800 number to call if you have a problem (last trip, one of the kiosks ate my battery. Called the 800 number & gave the kiosk #, and they reset it remotely & had it dispense the new battery - no hold time, it was very fast and easy)