I have come across flushing systems in the past that did not comply with water bye law. I think they were american. Basically a pipe from a CWSC to the flush connection of pan and a non concussive valve fitted in-line on a 1" pipe. If my memory is correct. A WC cistern was known as a waste water preventer with overflow to make people aware of any ball valve issues. The device mentioned may well be compliant as any filling malfunction can now be diverted to WC pan.