I am thinking about installing a tankless hot water heater and am somewhat hesitant. I live in New Jersey, where it can really get cold. Does anyone have any experience with these heaters? Can more than 1 person take a shower at the same time?

10 people can take a shower if you buy a unit that has enough gallon per minute water flow. And of course you have that much volume of water to start with.

Issues of water pressure, and volume all can effect the usage. The system is nothing new at all, it is the same principle that steam pressure washers have used for a decade or more.

And are you going to install a inside or outside unit , the type of unit, the water flow you have, and more all effects this

Are you asking information on a single fixture tankless or a whole house unit? While a tankless is more expensive to purchase they will pay for themselves over the long run. Cheers, Tom