Thanks for that, David!
In response to Nick. Perhaps I should have rephrased my post slightly. With a baby on board, my attitude to certain risks has changed.
So here goes...
I'm of the opinion that there must be a better way regarding expansion vessels and if this type of vessel works as is described then I'd be interested in fitting one (or two). I would be glad to hear from anyone who has any experience with this type of vessel or anyone who can anticipate any issues with its use.