I have had a Bosch for over 10 years with no problems. It runs on Natural gas. I have it in the attic where the original tank type water heater was. Its a gem. Since I go back and forth to the ranch for 4 or 5 days at a time, it saves me a bundle not having to keep hot water while I'm away. Mine has a thermostat so you can really turn it up if you like but can be dangerous for someone not aware of how hot the water can get.
The cons are the price and installation costs although I installed mine myself. You need natural gas or propane close by plus since they burn very hot you might have to enlarge the exhaust pipe like I did.
The Bosch are expensive but last a long time and should pay back a lot of their cost through energy savings.
I have two propane powered ones. One for the house and one in an apartment. The initial costs are more but never running out of hot water is a major plus and you will save in the long run because they have no pilot light. Also, they have electronic ignition so no electricity, no hot water. If you can call it a con it would be that they need cleaning out every year by running vinegar water thru them to clean out mineral deposits. Make sure your installer installs the necessary valves to do that.