Re: Targetting the ignorant?
" I'd not even have thought about making my own until you mentioned it. "
Sodium percarbonate is readily available as a cleaning supply and it's one of the cases of being hard to overdo it ("too much" will simply not break down into peroxide), but as mentioned it's usually easier just to buy it - with the caveat that you should look at the percentages as these powders range from 2% percarbonate up to 30%+ - and pricing gives no indication of concentration (the most heavily marketed ones tend to have less active ingredient, surprise surprise)
So far I've found that the best "bang per buck" is Tesco's own-brand "colours" oxy powder at 35% - but they also have a nearly identical package "whites" package which is 5% and only a couple of pence cheaper.
Coming back on topic - you could buy the lower concentration version or just use less of the other product - THIS is marketing at work - convincing you that you need 2 different products which turn out to be the same thing with different quantities of filler inserted.