I think Optimum has the best prices for clay alternatives but I think they come in a smaller size. I only have their "heavy/aggressive" towel and I don't think much of it though and rarely use it. I'm not sure if the "fine" grade is any better, but I haven't heard any complaints about it.
Nanoskin also has the Autoscrub Speedy Prep Sponge which is less pricy, and also smaller. I also have and use the one OTC clay mitt that is available and it works very well and is priced well.
Yes, they do have the potential to mar the paint, but so does traditional clay. It does depend somewhat on the paint that it is being used on. Just keep em lubed up and use very little pressure. Most here recommend that if you are going to clay, too at least follow it up with a light polishing.
