They work, but compressed fiberglass works too, and for less money.
They've got to have rockwool or mineral wool where you're at, Ray, if not some 703 or equivalent, don't they?
IIWY, I'd score rockwoll and make up some triangles to stack floor to ceiling in the corners, leaving three or four inches of space between the wall and the 'wool. You can cover with a frame of light wood and burlap.
To make the triangles, take a sheet of rockwool, and cut it in half with a serrated knife. An electric carving knife works perfectly. You should now have two squares instead of one rectangle.
Take each square and cut it diagonally into two triangles. You're done. You'll see immediately how 703 is easier to stack than rockwool, which is still kind of fluffy. Being patient with your cuts will go a long way towards getting them to stay afloat while you're building up.
You should be using rockwool in the 3.5-8 pounds per cubic foot range.
These types of traps would whup ass up on some foam.