I have that Cateye 1000 on the seatpost of my commuter. It's great and very bright. I've never tried to move it or mount it anywhere else. It's there year 'round....set it and forget it.
I had a Vistalight (don't recall which one) that I used to mount to the daisy chain around my panniers (Performance brand), but it disappeared on day. I don't know if someone lifted it in the parking garage where I lock my bike, or if it went flying during the ride home.
I prefer the secure mount of the seatpost, so long as your saddlebag or panniers don't block it.
I've been pondering that mini Cateye with the rope attachment - http://www.performancebike.com/shop/...slisearch=true - to put on the zipper of my REI sling bag for a light high-up.