I did about a year for a DTW area based 121 supplemental. The people were great for the most part, the flying was decent, the airplanes (while old) were in good shape. But for quality of life, money and just career progression (which you may or may not care aboue), getting into the regional game made life so much better. Sitting around within the callout period of whatever airline you fly for, 24/7 while you're on call, gets very old quick. You can't do whatever you want, because you're tethered to the phone. I made more money year 1 at a regional than I did in year 1 at a supplemental on a DC9.

Now, if you happen to live where one of these adhoc carrier is based and you don't care about moving on from there, the game changes slightly, but you can only polish a turd so much