No personal experience but spoke to plenty who did. Sounds like if you’re out in the country, they work fine. If you’re in town, then the boundaries are too wishy washy. Can’t recall what specific units they were all using though.
My parents have the Pathfinder collar and that only alerts you to a dog nearing or breaking a boundary. I think another had tried a brand called Halo. They said there was some delay and it didn’t work well in a crowded neighborhood.
I really like the idea of a GPS boundary for use while camping but I just use my GPS hunting collar and that seems to work well enough as long as I keep an eye on things.