where I'm based (US), supervised solo is purely and simply, observing from the ground with a handheld, anything more is doing the student a disservice in the long term, and is also ILLEGAL!!
We charge dual time for it, as correctly stated earlier, you're flying on the instructors licence and they're spending time on the ground observing.
What an arrogant post from Head Turner that I can only attribute to dangling the bait, as I hope no-one holds that view in reality.