You're not returning your kitchen oven because of temp variations are you ? Most don't even agree with a good therm. Some can be adjusted within a narrow window but still may not totally agree with the therm.
Water heaters, furnaces ect (gas or electric) the same way. They all have over shoot.
The MES was not designed specifically for some of the uses many of us are asking of it. Hence the Mods we do to them.
Smoking butts, ribs, chicken and such a little over shoot is inconsequential. Now when you cook some sausages i.e. Summer Sauasge you are flirting with temps where the fat will melt out of the meat mix and collect between the meat and casing. Not a good eating experience. This is where the PID's come in. They will allow for a much smaller window of over shoot, but not necessary if you want to wait it out at a lower setting to avoid the over shoot taking you into the fat out territory.
I know there are better electrics out there that have better control, but they cost more than MES with mods, a lot more.
The MES 30 and 40's are entry level smokers. The design has lent itself very well to being upgraded to a top performer. Most of us understood this fact very well when we bought them.
Many of us see it as no different than buying a car or truck and then adding nicer wheels, window tint, pinstriping, new sound system, bed cover, lift kit, trailer hitch, on and on.
Point is it is a base unit that you can make do whatever you want it to do for a relatively low investment. Yes it has flaws, but what do you expect for a cheap entry level unit of anything.
Many of these flaws may exist in you commercial smoker if you look well enough. Temp swings won't even show on a dial therm if that is what it has.
Gas units have a hard time in low temp smokes. The burners just aren't designed for that small of a flame and not easily blow out. You could be there a long time trying to get the temp just right. There are work arounds, but that puts right back where you didn't want to be with a cheap electric.