Just to chime in: I use this
all the time in testing, and it's never failed on me. You have to do the right thing in your app to watch for these changes and gracefully reset and all, but I've nuked the container (from Settings->iCloud, on Mac and iOS) dozens of times now and never had permanent breakage of any kind.
Occasionally, after doing this, it'll appear to take much longer to provision a new ubiquity store (sometimes minutes, which is unacceptable), but never actually broken.