The Phaart Bleep? I've got two and find them great. I had a small issue a few days ago when the lens came unstuck as I opened one of them to get the batteries out for charging, but a dab of superglue has sorted that.
Other than that I've been impressed with the brightness and find that the batteries last well between charges (I'm using 1000mAH NIMH cells). I think they are value for money.
The standard mount has a lot of adjustment so they should fit fine on an oversized seatpost.
Edit: linked to the thread from "what's new" without noting what section it was in. Oops, sorry.
