Tough. Pork butt is such a forgiving cut. At 250 I haven’t had a problem with tough exterior. Maybe it depends on the smoker and temp levels. I’ve seen a lot of smokers with gauges that don’t give an accurate smoker temp and run hotter than the reading. If your cooking at 300 then it can get tough exterior. Running at 250 or less and you shouldn’t have a problem at all.