They require regular maintenance, which is a key to any successful backcountry system. I wouldn't consider any system that handles this many people to be a "breeze" including picking up wag bags left behind on the trail and in bushes. They use 2 llamas on a weekly basis at Long's Peak. Yosemite uses mules for their maintenance.

If you've ever used the modern solar toilets at Yosemite's Nevada Falls, or Little Yosemite Valley, or the Grand Canyon (or at some other modern design) you know this system can work very well. It's more challenging at higher elevation, but it can be done successfully.