I did the JMT a few years ago and used the Garcia can. I've yet to see any other bear canister approved by the Forest Service/Park Service. I saw very few bear lockers along the JMT, but I did research ahead of time where they were. I tended to camp at higher elevations that were less populated, and the lockers are generally around very populated areas such as Rae Lakes. Because I camped higher, hanging my food wasn't often an option. There's always the Ray Jardine way of cooking dinner and then hiking more miles before camping, so the bears can't smell your food. The ursack might be a good option in this case. I preferred just having the can so I could sleep at night and not worry about losing my food. The only time a bear came into my camp was in Yosemite, at the base of Donohue Pass.
I use GG's Nimbus Ozone, and the can fits inside the pack on the very bottom (I prefer to not have a lot of things on the outside of my pack). I'm able to stuff clothes around it, so there isn't any wasted space, and it has worked fine.