In that case, I would assume they’re talking about how cold the incoming water would be.

I used a tankless in a zone five area where our incoming water in the winter was often below 60 degrees. You’ll have to compare the charts of input temp and output GPH to determine how it would work for your specific use case.

I used an indoor mounted one, but there are tankless models intended for places like CA and AZ where they can be mounted outside.

We liked the endless hot water - we only had one bath and three people, so we offer were bumping against the 60 gallons of our old tank model.