I've been using the Mother's Speed Clay for a few years and have been quite happy with it. I find it to be far easier than natural clay for two reasons: (1) with natural clay, if you happen to drop a piece, you theoretically have to throw that piece away, while with synthetic clay, you can rinse/wipe it off and keep going and (2) with natural clay, the traditional method calls for lubing the surface with quick detail, and with the synthetic clay I chose to use a bucket of regular car detergent (or strip wash) at higher concentration and proceed to "wash" the car a second time using the Speed Clay instead of a sponge or mit--with light pressure and checking for smoothness as I went.
Lately, I've followed the advice of Pan and others to treat the paint with iron remover before using the clay. It has really upped my game, making the clay process easier and ending with an even more decontaminated surface afterward.
Just in case it wasn't evident already, after using clay of any kind it's important to add a protective barrier back on the car, whether in the form of wax, coating, or sealant.
Edit: also wanted to point out that there are newer synthetic clay towel products that have a more matrix-like surface that are supposed to be gentler on the surface than traditional synthetic clay towels or synthetic clay pads like the Mother's Speed Clay. I purchased one made by Optimum products (they also make ONR) but haven't tried it yet.