I've never done a field escharotomy, but I have been trained to do it. It really is one of those very rare, maybe never done in a career, but when it's needed... type of procedures. A flight crew that I worked with quite frequently has done a couple over the years and they were exactly that kind of "oh crap" kind of circumferential burn scenarios where the skin is quite well cooked and doesn't allow chest expansion.
In my current role, I doubt I'll ever do one outside of a seriously major disaster and even then that's a maybe.