It's a hopper set up that's used for premudding paperfaced corner bead. Check with your local drywall supply house. Pla-Cor is the manufacturer here's a link to their site that shows a pic of the hopper.
http://pla-cor.com/MAIN/
You also need to buy the roller, you can get replacement rollers to do bullnosed bead as well.
This system is slicker than owlsh!t. All you do is fill the hopper with properly mixed mud, (I recommend using setting type compound, but work fast & clean out the hopper & rollers right away when you're finished with them for the day) Anyway once the hopper filled with mud, you run the bead thru the bottom, the black rubber gaskets you see in the bottom of the hopper will allow the correct amount of mud to go on the bead. Then you place it on the corners, and press it into place, Then grab your roller and embed the bead. Wipe both sides of the corner with a 6" knife & you're done with bead setting & first coat on the corner. If the board has been hung right, you can get by with one more coat and the corner is completely finished!! By hung right I mean the butt end of the board should just flush to the
back side of the board on the other wall at the corner
Took me about 30 mins to get used to it and it's a real time saver. We just finished a 3 story custom house, lots of outside corners, all bull nosed, seems like it was close to 700' of bead all told in the place. Helper was sick the day I ran bead and I was still finished setting all bead in the house before 2pm. It would have taken me nearly that long just to cinch the bead using regular metal bead & a cincher tool, then I still would have had to mud it all.
Don't know about current pricing, but when I bought my set-up I got the hopper, outside roller with rollers for 90 degree, splayed, & bullnosed angles & spent around $200 thru Negwer Supply in Columbia, MO.
They also make vinyl bead products as well and they have conversions pieces to go from from bull-nosed to 90 degree angles when you need them. Pretty sure you can order direct from the company from their site as well, but once I saw the system being used on a job I was sold, went right over the the supply house the next day & bought me one.