I quite like having a mattifying top coat as it means that you don't have to go out and buy all sorts of new polishes just for a certain finish. The top coat works really quickly at mattifying and dries fast too. I would say that the matte finish is at its best for around 24 hours and then begins to loose its finish.
I think its good enough as a matte top coat for the price and cheap enough to experiment with and help you decide if you like the effect of a matte polish or not.
I haven't made my mind up about the whole nail being matte but using it for a bit of nail art is nice.
10ml - £1.50