It is a very nice add on, but is definitely not necessary.
I have smoked a lot of snack sticks, jerky, butts, poultry, cheese etc. And haven't sprung for the Auber yet nor have I thought that my results suffered. The temp swings are not a big deal for sausages.
The one exception I would make is for fish. A 20 degree swing on fish can be a really big deal.
Aubers have more advantages than just for controlling temp swings. You can program various steps. For example, maybe you want to smoke at 140 degrees for 45 minutes, then increase the temp to 225 degrees, to an internal temp of 190 degrees, and then reduce the temp to 140 degrees and hold. You have four steps in this example that can each be automatically programmed.