(Potentially) underrated products: Hair chalk

On christmas, I was lucky enough to recieve something I have been curious about for quite some time: Hair chalk. Just rub it on some damp hair, and hey ho, you've got a new hair colour!
There's better versions out there than the one I received, I am led to believe, like the Colour (color?) bug bye Kevin Murphy. I've tried it out, and it's fabulous, but I can only ever afford one colour at a time- but surely the point of this kind of thing is being able to change your hair colour every day, or have heaps of colours in at once?
I'm pretty pleased with these bad boys- the only problem is that they can make my already brittle hair even more so, resulting in non compliant hair when you're trying to style it. Lucky for me, I'm a fan of an explosive hairdo. I dare say if your hair hasn't been ravaged by years of dyeing, it'll hold up just fine.