Depends. If your truck is going to sit more than you drive it, as in you won't need tires replaced for many many years, and you are located somewhere that hot sun is an issue, then they are probably worth it. If you actually put miles on your rig and are going to wear the tires out in short order anyway, why bother? You usually only see those on rv's that spend more time sitting still than driving. My 2 cents worth anyway.
You could do the rough math, figure out how much a set of tires cost, then make some assumption as to how much longer the uv protection adds to the life of the tires. Let's say your rig gets few enough miles that the tires will literally dry rot before you wear them out. And then for arguments sake say a set of good tires costs $2000. So if your tires would have dry rotted in a decade, and the covers stretch that life to 12 years, then that's a 20% improvement on the $2000 tire life means the covers are worth $400. Minus the pain in the ass always taking them on and off, and then you are covering up all your nice bling you paid extra for.
I do have some second hand experience on tire covers. I bought a 9 year old gooseneck triaxle enclosed trailer that still had like new tread on the original tires. Northern climate, bought in pristine condition from an extremely "particular" (read: anal) previous owner that had tire covers on it (he claimed to have always used them and I believe him). All 6 tires showed some signs of dry rot cracking, and proceeded to blow out one at a time as soon as the weather warmed up and tire temps climb. After the third tire blew I went out and replaced all that were left as well as the spare. End of tire problems.
So in my limited experience they were a waste of the previous owners time. But the old rv guys swear by them. Or maybe they're just retired and bored and need more to do when they set up camp. lol.