Yes they are worthless; it is surprising simple to get them cross threaded (rendering them useless). That has never happened with my brass plug (that's my research and development). To each there own.
If the RV industry's research and development was the "be all end all" then we wouldn't have so many threads about china bombs, leaks, stabilizing, parts falling off, furnaces malfunctioning, refrigerators that won't cool, window latches that don't latch, slides that don't slide, and warranties that are good for one year or the end of the dealers driveway whichever comes first.
Did you ever wonder why when you go to the RV store to pick up a new nylon plug (after the old one fails) they sell them on cards of two?