I use it all the time. Great flat finish. Top tips from Bob would be:
1. Store it upside down and only use what collects in the cap or neck if the bottle.
2. Don't use too much, and don't over work it. Just slap it on and leave it.
3. Try to avoid extremes of temperature when using it.
4. Don't shake it like it says on the bottle. If you move it, let it rest and settle again before using.
5. Be prepared to lose about a third of the bottle. If you only use the settled stuff as above, the Matting agent will get used up before the carrier liquid.
That said, it lasts for ages as you don't need much and compared to "proper" miniature varnish it's as cheap as my sister.
In short, I really like it.