According to Andy (Cutler), all the research into alpha lipoic acid as a chelator is based on the use of the synthetic S-ALA. He advises against the use of R-lipoic acid purely as there is no/not enough (can't remember which) research on it. I have come across some websites which describe R-ALA as a chelator though.
I agree with you that my preference would have been for something more natural but Andy's suggestion that it means basically experimenting on oneself put me off.
I have Kirkmans which actually doesn't say which one it is on the label, just 'alpha lipoic acid' but I assume it's the S version as a lot of people use it.