i think you would be surprized £20 is not a lot of mony to some people not to have the headache of ros and what money you can make with that out lay, iam surprized but thats the feed back iam getting.
though to be fair, you did post on here about it, and you will have opinions
my opinion
at the prices you have mentioned , people will be better off buying a smallish RO / DI unit and it will pay for itself in 2 weeks ( at 200 L per day )
now you replied to my post, with a few points
start up costs, 100 quid for a RO / DI unit, its not going to break the bank
100 floor flat, fair call, i would hazard a guess that they are few and far between, i know on the DIY forum i helped some1 who lived in a 4th floor flat
dont know how to fit them, i dont buy this, they come with instructions and its very easy to understand, they even come with self cutting taps
dont want to bother, now this could be it, they might be happy with paying 30 quid every 2 or 3 days, but reading the above points, they are just wasting money
as you say though, who are we to ask, i would ask them and point them in the right direction, but thats because thats the type of guy i am,
if you can make that sort of money from them, fair enough, good on you