Once it dries, it's completely matte, which looks a bit weird if your base colour is glossy, but you can easily rectify this by either using a glossy topcoat over everything (which is what I've done) or by using a matte base colour (or a matte topcoat). I think either way looks cool.
Base Color - Models Own Coral Reef, Topcoat - Nails Inc Kensington Caviar.
Despite the tricky application process though, I'm liking this product; I wasn't sure of the effect at first but I've had it on for a couple of days and it's grown on me. I like that it's completely random each time and that it looks a bit grungey. It'd be cool if there was more colours; currently it's only available in black, but I'd love to see a white or nude version. As with all Barry M products, it's super cheap, at only £3.95, and the fact that you can use it over any base colour means that the possibilities are endless for different colour combos. Win!