Pay no mind to sour apples. Just take some mental notes from their responses with a grain of salt, and ultimately do what you want to do. Being a part-time sup CAN suck terribly. Or it can be pretty kosher. It can be both. It is what you make it.
Opportunity for growth is dependent on your district. With that being said, there are HUGE amounts of middle and upper management retiring within the next couple of years, so there's almost a certainty that there will be better opportunities for Part-time sups to move up than there has been over the past 6 years or so.
The money is better initially. You would be making more over a long period of time if you stay an hourly, but if you need the money NOW, then by all means do it.
Job security is pretty solid for PT sups. When
hits the fan, you might get bitched at by your full-timer, but it's the full-timer that will be taking the heat from above. Upper management doesn't typically accept the excuse of "the part timer did it"....that will get thrown right back in the face of whatever FT sup decided to use it. I've been on many a conference call where this has happened.
As far as my personal opinion goes on your particular situation....If you can't seem to handle the criticism from a forum full of the kind of people that will be working for you at some point, then you may need to reconsider your ability to lead, coach, council, and manage that same group of people. UPS has done a terrible job assessing the interpersonal relationship skills of their management team, and having one less
bag who lacks people-skills can only be looked at as a step in the right direction. Continue to
on your sorter, and don't add to the crappy image that UPS management has already created for itself.