I just switched from Oxymagic by Clorox to Oxyclean Versatile Free. Both work great but I have some observations:
1) I think that Oxymagic contains quite a bit more percarbonate than the Oxyclean. This is what you are paying $ for not the fillers.
2) Oxyclean Versatile Free contains a surfactant. This isnt a big deal as it helps with cleaning, however I think that they add it to make up for the lack of bubbles that would be evident from cutting back on the percarbonate. Again the percarbonate should be the meat of the formula.
3) Both work great.
I had seen an interesting post by BlindlemonLars that he is using straight percarbonate. I may start doing this and adding soda ash as needed to put the pH at 10-11.5 .
I think that companies are reformulating and skimping on the percarbonate to increase their margins.