Well, after 30 minutes or so of ham fisted drilling, screwing etc, they are on.
bwinton said they are tricky to install, wouldn't say that, but you do need to think carefully about where exactly to mount them, one thing not clear from the pictures, they have a bend molded in, which you flatten out when fastening the bottom screw. This means the inner latch gives a positive connection around the rack tube, which is then pulled back when pulling on the strap connector. Obvious when you look at the thing in your hand. I positioned them to line up with the existing straps, which on my old an well used Seratus panniers means the clips now sit nicely between where the tube doubles up at the front, and where they bend up at the back. it positions the bag slightly further back out of reach of my big feet, and they don't move forward when going over bumps when heavily loaded. Seems like a successful and worthwhile mod.

Hardest things were drilling out the old rivets, and drilling new holes without snagging the fabric.