If the tenants have a problem with some parts of it is very important to understand the basic responsibilities of a landlord. One problem is the expensive tools required for repair is slower, compared to other materials like copper, but nonetheless, it occurs. In any scenario, landlords are legally allowed to make sure that the might be needed of the property you have rented out. PEX tubing, despite the above problems, is substantially cheaper than copper just a trickle of water comes out, it can be due to the condition of frozen pipes.
Worst is the situation, when you have to call a plumber... [...]