I came across this product, and thought I'd give it a try, especially to cover a few grey roots. I have to say that it is very easy to use, and it works exactly as described. Overall, it's a very good product to use to cover gray and roots.
I'm a dark blonde (at least I think I am), and I couldn't give the product a 5th star because I don't think the color is at all blonde. It's really a light brown. I then tried the white version, for light or platinum hair, and it was way too light - aged me 40 years on the spot by putting white hair in.
I would love it if Bumble and Bumble could come up with a new shade in between light brown/"blondish" and white.
Note: I have dry hair, and since this is a powder it is definitely drying (it would be perfect for oily and thin hair). I'd be willing to put up with it, though, if I could get a shade that works with my color.