Why would you play $8.99kg for a product that does the same thing as a $2.89kg product. Because of it's environmental claims? The first one has Eco in the name and the second has Homebrand. Both of them have Sodium Pericarbonate as the active ingredient, neither of them have added phosphorous, the cheaper one has enzymes which could cause irritation for some people with allergies.

If you have skin allergies you might consider your own basic washing powder, so that you know what is in it. BTW 60% of both products is made up of bicarb of soda anyway.