I think there is something to be said about learning to control your cooker without the temp control. Plus WSMs really don't need it.
With that said, I do use a Stoker system on my 22 and 18 WSMs at comps. More than anything it lets me get some sleep without having to worry about temps.
Co-head cook of Smokin' Timbers BBQ
22.5 Weber Kettle Grey, 22.5 Weber Kettle Green, 22.5 WSM, Two 18.5 WSMs, Mini WSM, Weber Genesis Silver, 18.5 Smokey Joe Platinum with Pro Q Stacker, WeberImperial Sequoia, Charbroil Silver Smoker, Rib-o-lator, Green Thermapen, Stoker with wifi