I'm very impressed with this product. I bought the rail a few days ago - it was delivered promptly and in bomb-proof packaging.
To use it as a camera slider, you'll need a few other components. I bought a second-hand three-way tripod head for a few pounds, and I already had a duplicate quick release plate for my current tripod. First of all, I bolted this QR plate to the rail using the existing holes - this means I can mount it easily to my tripod. Then I drilled a 6mm hole through the centre of the sliding block. Using the tripod screw from the old QR plate, I bolted the second-hand head to the block. I added the camera to the head, and that was it - finished. Very quick, very easy, and very impressive results.
I'm glad I picked the 80mm rail - it's cheaper than the 60mm version, and I'm not sure the 40mm would be sturdy enough. This feels very robust, and there's no bow at all in the rail, even with a full-laden camera on one end. A word of warning - you should also invest in some clamps - you don't want your camera to drop off the end of the rail......
All-in-all, I'm very impressed. It needs a little work to convert into a DSLR slider, but I don't hesitate to give this five stars.