USE Sumo Clamp Kit

With this design you have to choose between squeezing your carbon rails too hard and get a well fixed saddle or save the rails, but be no certain if your saddle rotates during a ride.
Recommended torque is 10-12 Nm, while some rails can withstand only 7-8.
Also, it is prone to sticking after being tightened. I.e., if you torqued it to spec, it could be very hard to unstick the clamp and readjust your saddle.
Finally, my 9x7 version cracked after one racing season.

I recommend this product

I like the USE posts because it is possible with this 360 degree swivellable clamp to turn the post around and use the offset pointing forwards for a more Time Trial type position on a road bike.

The fact that there is only one bolt, which is also the axis of swivel means that USE have designed a way for it to be stable while only being tightened in one place. That is to use tapered shoulders that fit into the clamp that lock in place. This means that it is difficult to adjust the angle of the saddle because the clamp locks down so well. I have to remove the saddle to adjust.

The other disadvantage of the one bolt system is that the height of the channel for the saddle rails can't be adjusted, so the clamp can't be used on a variety of saddle rails, but rather one must purchase a clamp for each type of rail with a groove matching the rail dimensions. I have the basic round clamp and wonder whether to buy a 7mm x 9mm clamp for carbon rails on cheap Chinese saddles. I probably will.

I recommend this product

I wish I didn't have a USE seatpost but now that I do, I am not the only one that has had problems with it (google if you don't believe me). So I've had to shell out for a replacement clamp. SJS had the best price I could find but its still annoyingly expensive.

I recommend this product

3 years ago I bought the 7x9 version so I could use carbon railed saddles with my LOOK e-post. I used the regular 7mm round USE fitment for several years, no problems, but after 3 years the 7x9 developed a crack.