I ran my heater for half hour this morning and checked temperature(coiled hose)and it was reading just over 59c. Too hot to leave my hand under....
I've not fired it up for 12 days as I've been away. The smaller heaters probably won't get as hot and will lose a lot of heat in winter with hose out resulting in a less than satisfactory 'brush end' temperature.
The immersion heater keeps the hose warm etc in the winter so it heats your hands when moving it etc, tbh if it's absolutely freezing I'm not going out anyway, with or without hot water, I'm not loaded, but I've enough there which means me not going out in freezing conditions doesn't effect my life style money wise.
If it speeded things up and even managed to get you doing another £50 a week worth of work then I'd say it's a no brainer. For monthly domestic cleans it's not any faster.
For people who do commercial contracts on a 6 monthly basis etc, I think hot would probably shave some time from they kind of cleans. And although there probably wouldn't be to much a difference in time, if you do alot of that type of work then all of it added up over the year would add up to quite a bit.