By "testing" you mean.. showing what the image looks like at different sizes? I'm not seeing the point. Maybe I'm missing something though. Maybe changing the description line from "just upload your 512x512 icon image and we'll do the rest..." to something more explicit would help?

I agree, it's made for iPhone developers/designers so they can test their app icons on the device without having to deploy builds for each icon iteration... thanks for the feedback

MUCH better. You know what would be cool? If you implement an SMS service like Sendhub so people can text themselves the link. Just an idea..

that would be much more convenient, i'll look into it