My fairly recently acquired hot water heater has, in my humble opinion, allowed me to plough my way through first cleans much faster than I'm used to.
Normally, I would always use a detergent on a first clean, just for my own peace of mind, so that I would know, within reason, that the glass was free of any kind of nasties. But, as a consequence of this procedure, I would incur a rather lengthy time penalty; taking anywhere from three to five times the duration of a standard clean.
Anyway, a hot water heater has allowed me to clean first time customers in just twice the time it would normally take while still achieving the same standard as when I was using a detergent.
Nick