I put a tankless in the last house I had. I'd do it again in a minute. All the issues people complain about can be solves easily. (Like low flow. That's just the end on the faucet, so change it out.) We have hard city water, and I never had to clean it in at least the 8 years or so I lived in the house with it. (It's still in the house I know because my ex wife lives there.
) They are fantastic. But, yes, they are gas hungry. I did have gas pressure issues at the house after installing it, but ONLY when the furnace in the house, water heater and the furnace in the garage were all running at the same time. I had to learn to shut off the furnace in the garage before I got in the shower or it would really cool off.
I needed a larger meter/regulator. I had run large enough pipe, but the regulator wouldn't flow enough to keep up. My local gas company would have to switch it out. Don't let the gas company con you though, they will try to tell you that you have to go to a "commercial" meter. You tell them that's a crock of sh!t! Residential is residential, they just have to give you a larger regulator or meter. BTDT before.