I have had 2 Bosch Tankless water heaters- my house runs on propane. The first Bosch unit was a 250sx , and it was a real pos. Non stop headaches, but I was too cheap to replace it. It had to be reset twice a day, endless calls to Bosch for tech support and was never able to get it working perfectly, but it "mostly" worked, so I suffered along with it for 10 years. Eventually I spoke to somebody at a big tankless dealer and mentioned what I currently had, and he immediately mentioned 2-3 problems with it and pronounced it a POS without any prompting from me. After a long conversation he said "the newer Bosch units are far superior, the factory has far better QA" yada yada, so I replaced it with a Bosch Integra 500. A big selling point for me is that it was a plug and play install. He had the 2 other popular brands as well and could easily have sold me those. The guy I spoke with really knew his stuff.
Well, he was 100% correct- the Bosch 250sx was a lemon model- my Integra 500 worked the very first time, no adjustment needed, and has been flawless in the 2 years since I installed it. Pros: endless hot water, smaller space requirement, significant energy savings. Cons: higher price, higher install cost. I did my own installation which was typical plumbing work, but I had to cut a 4 " hole in brick for the exhaust which was a daunting task until I found you can rent equipment to do that job.