I have had a spool in mine for a little over a year now, and like it. I drive it to work quite a bit. It's predictable & was a cheap & easy to install option. Spools don't load up, so they won't jar your rig or pop, but the tires will bark on sharp low speed turns like parking lots or around town, but not bad.
I can't tell you how fast it will eat your tires up, though. I work less than 6 miles from home, and i don't drive it on long trips. I think i took it to my uncles in Camdenton once, John's a couple of times & Chadwick once or twice. I've probably gone a total of 2k miles since i installed it. You'd get more benefits from a front selectable than a rear. Your other option is just throw in a Loc-rite in the rear.