A heating engineer I know is working on sites installing Hep2O. O rings being dislodged after the pipe is installed is pretty common. The fitting failure rate is high averaging one every second house. It takes a hell of an effort to push these fitting home which the installers don't particularly like, especially in tight corners. In many instances a normal compression joint would be better. Many fittings fail after a test (all systems are pressure tested) and when the same fitting is taken off and replaced it holds. Small amounts of dust/dirt can make a leak.
None of them are too fussed on plastic pipe and think it is more of a hindrance because of the constant failures on the first fix. When they do a soldered joint they know it will hold. The odd compression joint weeping usually means just a quick tighten up. Installing copper on first fix is just as easy to these guys, if not easier than plastic pipe. Plastic requires more clips. They say it does not cut installation time.
Plastic Is only used so the Travellers will not strip out the copper overnight.
That is one of plastics advantages. It is resistant to freezing.