Q2) Would you think they are right?

I don't understand why you would do anything. The pressure
at my house is 80 psi, check it every once it awhile when it
seems the pressure is down. No expansion tank. Why do you
need one? The pressure relief valve on the hot water tank
takes care of protecting the hot water tank

The blow-off valve on the hot water tank is a safety feature.
It's not designed, and shouldn't be relied on, for frequent activation.
Expansion tanks are cheap insurance. Get one.