Thanks for all the replies.
I thought of hiring one for the day, they're about £60 though! That's really why I wanted your experiences. No point lashing out all that cash if it fails.... but it all sounds very encouraging.
I've heard of plugging the sysyem, it is a vented system, John T, unlike you and AJS I'm a bit of a girlie! More visions of Biblical floods

. Bunging the system, living life to the limits..... Is there no weep of water that will prevent soldering AJS?
Yes, I also wondered about working on each pipe, using both heads and freezing at a distance, as you say it stays frozen all the while the machine is plugged in.
The Freezemasters are expensive, especially if the thing breaks down or needs re-charging, I'm pleased you mentioned that. Forewarned and all!
So, thanks for taking the time and for the help, gents.
I went on an Aqualisa shower free day to-day. Brilliant... costs nothing lots of good information, free coffee and biscuits, free buffet lunch, a bag of goodies and some really cheap deals too.
I'm going to book the courses for digital showers and pumps. It was that good!
Terry H