I really have no expertise but everything I've read says the S-ALA which is a byproduct in making the R-ALA supplement is inactive and really doesn't do anything to help. I think it's just cheaper to leave it in instead of refine the product more to take out the S-ALA for a 100% R-ALA product. This article has an easier to read and understand explanation...

(R)-Lipoic Acid: Unique ‘Mitochondrial Antioxidant’ Fights Premature Aging: https://nutritionreview.org/2019/07/r-lipoic-acid-unique-mitochondrial-antioxidant-fights-premature-aging/

I wouldn't purchase the version with S-ALA even if it's cheaper, but that's just my opinion.