Hi all, I install a gas water heater for a couple of mths and I can help answer some questions. I am using the ferroli fe10. Most of the funny things are heard because people or id don't really understand how these things work. Heck even my contractor didn't know how it works. 1) will affect water pressure and will it be able to run a rain shower? despite the myths and all, it largely depends on your water pressure coming into the house. The heater will just pass thru this pressure (keep in mind the fe10 is meant for a whole house usage). My rain shower works fine. An instant heater will reduce your water pressure as it can't heat the water fast enough. 2) smoke appearing etc There is no smoke that appears. However it does produce some noise as it runs a pump when activated. There is also a slight smell of gas, similar to a gas stove. 3) slow to heat up, waste water etc this largely depends on your expectation especially if you have been using an instant water heater. Instant water heater will heat your water in 5-10 seconds at a reduced water pressure. Gas heaters similar to storage heater needs the water to flow quite a distance. My heater is in the service area and runs thru the house internal piping. It take roughly 20-30secs to get hot water. On top of that, the water if has been cold in the pipes and the heater is started, it will take another 5-10 secs to heat up the water. In comparsion to the storage heater, the storage heater u would need to turn it on way before you want to shower or use hot water. Also the savings you get from gas is quite a bit. In summary, an instant water heater is best if you don't need hot water in your whole house and don't need a rain shower. A gas heater is a cheap and convenient way to have hot water for the entire house. A storage heater if you don't have gas running in or you need to make up for the lack of water pressure. Hope this helps! I was in the same shoes as you guys and just decided to take the risk of getting a gas heater.