Odd that they would say that since ppm doesn't really work in a linear way like that. Otherwise we'd all be using 500 ppm silver (I've tried it and it didn't work at all). But ppm is confusing enough, so it's no doubt easier for the mfgs to let consumers have their own perceptions than explaining how sometimes less of the active ingredient is more powerful. Try selling THAT to the pulic. Very similar to how hard it is for homeopaths to explain themselves. Or high end amp makers that tell you 15 good watts is better than 400 not so good watts.
Often true, but I'd never want to be the one selling the 15 watt models for thousands of dollars.
Try it both ways and see for yourself. Personally 10ppm batches were both the strongest and easiest to tolerate for me.