We love our tankless. We boondock 80% of the time so know about conserving water. Our water consumption per week is exactly the same as when we had a tank heater.
We don't 'waste' anywhere near a gallon when adjusting temp. It takes us 10 seconds to get hot water and adjusted to correct temp. You'll get better at adjusting as you use your system more.
I believe some RVs have longer pipe runs between the heater and the shower, but that really isn't much water. One fellow who didn't want to waste any water would capture it in a bucket until he had the temp correct and pour it back into the fresh tank later. Sounds like way too much trouble to me
Give using your tankless some time and I bet it gets better. It took us several weeks to get used to the little differences. Also, get an Oxygenics original RV shower head to improve the water flow and general experience.
We enjoy our tankless so much we will always have one in any new unit we buy.
Good luck and enjoy.
Scott and Liz - Southern NM
2012 Wildcat Sterling 32RL - w/level up (best option ever)
2007 Chevy 2500HD 4dr short bed Duramax w/allison
Reese Fifth Airborne air ride king pin coupler with Sidewinder