My take on it is this....
those that have spent (shall I say a large amount - seeing as they are a bit prickly) on a hot water system have, on every occasion made it clear that any other form of producing hot is not only as good at cleaning as 'their' hot water but is either dangerous or done because those who choose other methods are some way a second class business.
If your circumstances are such you wish to buy a system there's no problem with that - but the benefits of hot are NOT massive they are marginal - definitely a would like to have as opposed to I need to have. they are more about making the job comfortable than cleaning better ( I have run various tests and time trials )
There is no way the investment in a heated system from grippa etc.. pays for itself within 8 years never mind 3 years so as a business decision it makes no sense - for a single operator possibly. But p&f is doing something fantastic - taking an air heater and turning it into an on demand water heater for what is a more attractive cost (lets face it the 'Webasto' systems are just a glorified conversion job.
Darran