I'm not that familar with Hobart, so I can't help you with any specifics, but it looks fairly old. What type of connector does it have? Do you have a Hobart machine? It's probably going to be specific to only a Hobart machine.
I've used a spoolgun a little, but I prefer a push/pull setup. The spoolguns are more affordable and they work just fine unless you need to get into tight places very often.
Ohhh....I thought it was one you had or were looking at. What push pull gun do you have for sale? I've got a CobraMatic I'd like to get rid of. I finally bought an Aluma Pro a couple months ago for my Miller 350P. That thing is sweet.
Yours looks a bit older than mine. I used mine for a few years and it worked OK, but I still had some feed issues. I believe some of that was due to the fact that my gun needed a couple parts replaced due to neglect from the PO. I just couldn't afford or justify spending the $600 for the parts on a gun that old. I need to get mine cleaned up and see if I can sell it. Good luck with yours.