They're here!

The bumpers arrived speedily from Dokken in MN! The bumpers do NOT have magnets attached, so some finagling with attachment options was required.  I tried two main versions, pictured below:

Attachment type 1: Metal D rings tied to ropes

Attachment type 1: The D rings worked ok, but there was so little metal in contact at any one time that they didn't stick very securely to the magnets on the arm of the rig. Tying required a lot of the rope as well, making the bumper hang a bit closer to the arm than I would've liked.

Attachment type 2: Metal rope clamps

Attachment type 2: This ended up being the method I stuck with - the clamps were a bit tricky to put on securely (you need tools, not just your own fingers LOL), but once on, the additional metal in contact with the magnet makes this more secure. I do still need to play around with magnet placement to ensure maximum contact on the arm, but it's serviceable for now.

A note to those using these bumpers - they are NOT very durable.  Kestrel had one in pieces within a few minutes of bringing it to shore after a retrieve. Make sure you have a good "drop it" with your dog or you will need to buy a gross. ;)