Not sure if I actually understand what is it about. I'd like to see HUSL colorpicker beside the rival ones (including HSV) to understand if it's really more useful. Random generated colors are nice indeed, but I'm always having a struggle with defining what I want from random, so I want to neglect this use-case.

I mean, I never can trust any studies that say "70% of respondents told us that these colors have brightness of 60%, although, technically speaking, this color is brighter that that, so it's a property of human eye to perceive these shades brighter than these" for several reasons. I can trust a physical definition of brightness, or as simple definition of color as RGB. There's real meaning to that. But what one actually means, when he says "this color is 60% bright"? It is totally a matter of his learning experience, that made his definition of "bright" to be what it is. If one spends enough time working with RGB, he can guess hex-codes closely enough, for him it would be intuitive, as his mental model of color was developed with RGB as a guide. But I doubt any newcomer can say RGB is "intuitive". Intuitive understanding of any tool comes with real experience of using it. So it's not about how intuitive tool looks, but how effective it is after you learn how to use it.

So, yeah, at a first glance HUSL looks "intuitive", but I cannot say if it's a good thing or a bad one, without actually trying to pick colors using that scheme.