>PEX is fine and easier to install than copper.<
To me the problem with PEX is its on a boat that may sit for a month or 6 ,(unlike most dirt houses) so whatever plasticizers are in the plastic tubing and fittings have plenty of time to leach out.
Just running the water for a few min will not clear this as the tubing is connected to the water tank, and HW heater.
AS copper tubing is common ,cheap and easy to work with or repair , I figure using the best is cheap insurance.($20,000 per day in the ER)
Same argument for running our 1996 Buick Roadmaster Estate Wagon at 20MPG rather than an econobox that gets 50 MPG .
At our miles a year the difference in fuel cost would take almost forever to pay for a single day after a car crash.
Prevention is cheaper than cure.