One issue that i've found with seatpost mounts is a lot of lateral sway, sometimes hitting the spokes, okay on a mountainbike, but a dissaster on a racer. Make sure you get one with a dropped part on either side, then secure that to the seatstay with clips or even cableties. I used a mixture of clips and coathangers (cut and bent to bridge the gap), as i wanted the rack up high. None of this is weightbearing, but it stops you from loosing spkes.