Put it in the bin!
It doesn't work, it blooms EVERY time. I have tried spraying it, brushing it, thinning it, useless, and I was looking forward to this stuff hitting the market. I have only used and tested product from the first batch that came out, so things may have improved, but is it worth the risk. My thoughts, there may be ten times the matting agent needed mixed in to it, just an observation based on my testing.
Try Humbrol Mattcote instead, this is enamel based, it can be a pig to stir all the sediment into suspension, but it seems to be a more reliable option. Also, thinning with a decent spray thinner, even for brush work, is very effective.
Also, I can confirm the Ronseal Mattcoat as being very effective, as Colin says, local ironmongers rather than the big DIY stores seem the best sources for this.