Hi Matt,
I have had a Masterclean inline heater for 2 weeks now. It was recommended to me by a trusted source, when I asked the same question you did.
I have raved about it elswhere. It is absolutely the Mutts Nuts

. I used to fill the Diamondback up with buckets of hot water from the tap but It was pretty much cold at the end of 50feet.
The first time I put the Masterclean heater in line I was amazed, the water was piping hot at the end of 50 feet of hose, even hotter when only using 25feet. It is definatley one of my best buys since starting up (and I've had a few good deals!) I bought it on Ebay for a fraction of the V2 steamate.
I have also run it continuously for up to three hours and it just keeps pumping out hot solution. I am going to measure the temp at the end of 50feet of hose and post the result when I get a chance but it is Hot, not scalding, but HOT,
I have seen a big improment in cleaning and drying times since I put it inline and I'm even considering buying a back up to have in the van whilst they're still going on Ebay. I made up an angle bracket to attach it to the porty at the back under the handle just as Prochem do with the heat n run.
BUY IT.......... if it's on EBay get bidding, if not phone Vernon at Masterclean, but get one, they are THAT good

Regards,
Adam