Just wondering if anyone has tried any of these commercial clay block paint oxide remover things... If so; do they work? Do they work on all paint types? Can I just use regular $1 a pound sculpting/pottery clay, or do I need the magic of the $20/150gram block at my local auto store?
Yes, they do work for what they're intended (removing contamination on the paint, overspray etc) and no, as far as I know they're not the same as pottery clay but have some other ingredients in them. Rubbing pottery clay on your car will more or less give you the same result as rubbing sand on it...
Keep in mind that using a clay bar only make sense as part of a full detail. You wash the car thoroughly, then you clay it, polish it, wax & seal it. Clay will not remove oxidised paint (that's not what it's intended use is) but it'll remove contaminants on the paint reasonably safely that so you don't end up either trying to remove it using polish or worse, scratch the paint while polishing. Clay also pretty much strips any existing wax and sealant off the paint so if you're not going through the full routine you're likely to make things worse, not better.
I have tried it many years ago on an Imron paint job. The finish felt smoother than before and the sliding rag test was better. I didn't see any visual difference. In after thought I wondered about the grit that the clay is picking up. Since you reuse the clay wouldn't the clay hold the grit and eventually act as an abrasive? It appeared to do no harm but I didn't think the results justified the effort.