This kit appears to be what was originally the 'Plumbfreeze FZ400' from Plumbfreeze but rehoused (and possibly modified?). Plumbfreeze told me at that time that they planned to sell out to a 'big concern' -- I guess it was Rothenberger (?)
I bought one of the originals on special introductory offer at about £250 but returned it because it didn't work! There was quite a discussion on this forum at the time. Turned out to be a 'rogue' unit, though! A bit of plastic had apparently come loose inside and partially blocked the head cooling fluid pipework. Hopefully they have improved the internal design since then.
The suppliers told me that the heat-conducting 'paste', is petroleum jelly (e.g. 'vaseline), so you can use that if you wish. Alternatively, you could wrap the pipe with a single layer of thin wet cloth before applying the clamp. This always works well with conventional freezers at anyrate.
If you do a lot of pipework it may pay in the long run to have an electric freezing kit - clearing airlocks can take ages after draindowns. But I would always keep a cheap canister-type freezing kit in the van as well. The big advantage with these is that you can manoeuvre the soft freezing mufflers into much tighter and inaccessible corners than the bigger, more rigid, electric heads. This can sometimes save the day!
As for the cost of the canister freezing fluid -- charge it to the customer of course! You're saving him labour costs after all, aren't you? (I charge £4 per 100g of fluid used.)