Come on hours and hours to get the kind of temp I get in 10 minutes and then get it constantly for as long as I so wish,what happens if you heat the water up all night and then the next day for whatever reason you don’t work what a waste.
It's not like the hrs heating you could have been cleaning - it gets heated overnight.
As for the not working, well its a couple of quid wasted. How much did your hot system cost and how much to service it?
I don't have an issue with diesel heaters at all but immersion heaters are a great cheap way of getting warm water if you have power close by.
I freely admit virtually instant hot water is useful but I'm not sure I would pay the high price for it. It takes a lot of extra jobs to recoup the outlay.
Every business is different and everyone works out returns on investment and ease of use differently, no right or wrong.