Annie, the plastic valves haven't improved over the years. I have one on our '08 fresh water tank. The first one was nearly impossible to turn; was replaced under warranty, was easy, then became hard. Bring a wrench when you crawl under to give you some leverage. But when you sanitize the tank, and then repeatedly flush, you'll doing a lot of crawling underneath to open and close the valve. I'm sure another, better valve could be installed in a better place, but have no experience with that.
Strangely, the water lines have two metal drain valves with a wing nut like object to open them. It's the same kind of valve used on auto and truck radiators. They can stick too, but work better than the cheesy plastic ones.