Pex has been used long term in Europe but since the demise of polybutylene, it doesn't have the long term experience in the U.S. for anyone to say much about. It is used around here on about all new installations because of its ease of installation and repair. Even copper pipe has lots of problems with pin holes in areas with corrosive water or through electrolysis. Get something in writing from your plumber about the warranty and his recommendations on reliability. Maybe the plumbers need to meet with the realtors on this.
PB had its legal problems but many houses around here are plumbed with it without problems as long as copper fittings and crimp rings were used. Vanguard pipe didn't really have much trouble except for the "service blue" pb used from the meter to the house which got splits in it. The pb lawsuit started over bad fittings and I keep hearing bad things about Quest brand pipe and fittings in the lawsuits although you go to about any hardware/big box/home cheap store and they all still sell Quest fittings so go figure. One problem pb had which pex may also have, is exposure to the sun cause UV rays will eat it up. The pipe shouldn't be stored outside for more than 30 days so I would avoid a plumber/retailer/wholesaler/middleman who may have stored it outside which is a process that you can't control with big box stores (go out behind one and you see about anything and everything setting on pallets) but plumbers who stand behind their warranties should be watchful of where their pipe comes from and how their wholesalers store it.
Proof is in the pudding and there are plenty of houses around here with pb and pex that don't have any problems if someone wants to go inspect them. The realtors around here don't worry about either but it is something to disclose that is present if they want to cya. Good luck.