I have the aquarack that mounts to the saddle. It's not as nice as the one that clamps to the post. It's pretty much all plastic. The pivot where you adjust the angle of the bottles slips. It's plastic on plastic contact. I'm cranking the bolt down ride after ride and it's getting better, but I'm afraid to go to far and crack/snap the plastic. I bought mine a while back ago, I don't know if they changed the design since then.

If I was to do it again, I would buy something like the minoura bracket. Just my 2 cents.