On my Traeger Junior, I had put a generic PID on it, I was never really able to get the PID to hold a temperature as well as I'd like it too, and I wound up resorting to using it as a manual feed rate adjustment device. Generally speaking, it's actually not really that big of a deal to just dial in the temperature you want, by adjusting the feed rate, then leaving it run at that feed rate. I have done many long cook with it that way. In some ways I prefer it actually over holding a set temperature... As long as don't get any drastic changes in weather during the cook , there's actually very little reason to keep adjusting the feed rate of a pellet grill. The reason , I sometimes preferred setting a feed rate and letting it go, is because what typically happens, is as the meat's internal temperature rises, the temperature inside the grill also rises... So lets say you start out at 225F, weather doesn't change much, but your big hunk of pork butt warms up inside the grill, eventually the grill temperature rises as the meat temperature rises, and by the end of the cook your grill's temperature might be up to 275F, which by that time, your meat was in a stall anyway, the additional heat helps motor through the stall...
So anyway, I actually don't see a big issue with a constant feed rate for 90% of what I cook, never been one to demand ultra tight cooking temperatures.