I’d say that’s the downside of these. Depends too on how close the faucet is to the heater. Same as a traditional heater there. In my unit the shower and bathroom sink get warm pretty quick, but kitchen takes some time.
Some have a flow adjustment on them. My Furion does. Set to max. I’m thinking that would allow a larger volume of hot to mix with the cold. I’m still learning about it though. May be wrong there.
Absolutely wastes water and holding tank capacity. Not good when dry camping. I hated mine so much I swapped it out for a tank model. Couldn't be happier.
Yes, I have one in my house. Every time you turn on the hot water faucet, the burner must purge the flame chamber, before the burner can light. This takes a couple seconds.