I've climbed on a Blair for years. I've briefly tried a friend's BF. I'm sticking with the Blair. There are definite advantages to the BF (replaceable bridge, light weight to name a couple) and I obviously can't say much about it from such a short trial.
I like the UL because it is completely modular. I can pull out the belt, toss the snap hooks, and put on as many rings as I want. I can add a ditty bag directly to the belt so I know where it is and which direction it's hanging. I can replace the separate leg straps with a bottom half that uses a different system or just replace worn-out straps with the same system. I like the large side 'D' rings for clipping in two lanyards at once (I use a double-ended) (I wouldn't mind if the two sliding 'D's were smaller, but ya can't have everything). All for something like $50 less than the BF.
I'll be tough to sway toward another saddle any time soon.
k