I have put four Bosch on-demand water heaters into use on my own properties. They worked GREAT for me when:
1) Setting the temperature all the way to the top or almost all the way...when the temp is set to the mid-range, the water takes forever to warm the pipes, before it gets to you, so you might not find it hot enough, but be certain not to deliver scalding water. About 100 to 102 degrees F is a good shower temp.
2) Allowing for the time, energy, and expense and PITA of installing a 5 inch flue all the way up and the additional height it might need.
3) Removing flow restrictors from the shower and faucet heads...this helps a lot, especially in sinks. You must have a lot of flow to turn it on. Don't expect warm water when trickling from the hot faucet...you won't get it. Most faucets will have to be turned on at least 75% of max to get hot water.
4) Lots of GPM helps in general..3/4 water supply line with a minimum of 40GPM, and 50 would be better.
I have used both the LP and Propane versions. I love these things and have never had a leak.