Perhaps the “need” for this device is because once you have tied a knot in the bag, it makes it more difficult to tie up the bag when it is full. Untying the “sizing” knot is not always easy.
Just a thought. Overall, it looks pretty silly.
I swear, I didn’t read Clanger or Duke’s responses before I posted. It was Craftermans tips that got me thinking…
I has the window open since about 8:30 and didn’t preview when I posted.
Really. :dubious:
Uncommon Sense got the procedure exactly right. When I had a trash bag )or “can liner” as it is called in the industry), I would split it about 6" and tie a tight knot and it would hold just fine. I can easily imagine these things being tossed out with the bag. At $1.50 a pop, that would get expensive.
I think Uncommon Sense was much more correct than I was. I was thinking more along the lines of something to twist the top of an already full bag that was in a can so it could be tied off since you couldn’t spin the whole bag. The use US outlines, and you confirm, isn’t really what I had in mind.
I knew it!
Sorta.
I had an inkling it was trash, but…
Do another one!!!
Glad to be of service… 
Watched them used for clinical waste incineration, I used to maintain the incinerators.
I saw that there’s been an answer, but it also looks a hell of a lot like a portable spoke wrench that I could never figure out how the hell to use.
I read Uncommon Sense’s description of how it’s used several times, and can’t get a mental picture. Can you take a picture of it in use?
And I still say you can open a beer bottle with it, too.
The metal is too thin to open a bottle, however.
You’re just not trying hard enough. 
Thanks for the picture.