Dullcote is a pretty "hot" lacquer though, so I'd test it somewhere unobtrusive first. I've had some interesting interactions with other clear finishes (don't use it over Tamiya clear gloss!), have seen it wrinkle acrylic metallics, and it can be pretty unfriendly to ALPS printed decals. Light, thin coats only!

I've also had poor results with Mr Hobby flat coat. If I were matt varnishing a competition model I'd use Tamiya gloss then Tamiya matt. Pretty expensive for my Epic collection though.