I purchased a new Bosch 125B NG for about $300 on a great sale. It replaced my old 40gal tank heater from the early 1990's that was starting to leak. On the whole, I could not be happier with the unit. My wife and I are thrilled! But, as others have stated here, people who consider one need to understand just what they are getting.

First off, there is more work involved in the installation. No question. If you are a competent DIY who can plumb, run duct work, and follow instuctions and codes, you will be fine.

  In my case I was replumbing the whole house at the same time, so it was not a big deal to reroute the tubing for a tankless unit. I used 3/4" PEX up until the required distance from the heater and then all 3/4" brass tubing, fittings, and valves up to the heater's lines. The water accelerates going through the heater so it pays to supply it with more than 1/2" water lines, even though it is 1/2" right at the stainless inlets. In the same vein, 3/4" black gas piping right up to the heater inlet helps insure an adequate supply, don't skimp on the gas!  

I also side vented the unit (to eventually remove our aging chimney altogether), so I purchased and installed the AQ1 power vent kit. (another $300!) This is actually more work than the heater itself to install, as it has Very Specific installation requirements and clearances to combustibles. But the kit instructions are adequate; if you follow these and the codes you will have no trouble.

 This is not a heater for larger homes! (depending on your definition, I suppose) Our home is an great candidate for a heater of this size. A small 2 story bungalow, maybe 900 square feet, with a basement bathroom/washroom, kitchen directly above with a sink, and 2nd floor bathroom directly above that. No singe pipe run in the house is more than 20'. From the time you open up a faucet, you have at most 4 seconds till the water gets warm, and maybe another 3 until it is quite hot. 

 You should not expect to run more that 1 hot major water application at a time. Two sinks is fine, but showers and washers should be run sequentially. That being said, you can take as long of a shower as you like. :) Even flushing toilets only drops the pressure slightly; the temp does not change. And in a smaller home, the space savings are wonderful. The heater itself is basically a box, only 30" high, 18" wide, and about 7" deep. It's about the size of a modest flat-panel TV hung on the wall vertically, only thicker. 

Finally, there is maintenance involved in keeping this heater going. You need to perform periodic inspections and possible part replacements, depending on what you find. But if you are used to performing routine maintenence (which Every appliance should have, just like your car), the checklist is small and the tasks are straightforward.

On the whole, a great heater for the size and capacity.

Recommended: Yes