What's so great about it?
The strongest way to seal minis is to use a paint on gloss varnish and then cover with a matte varnish (assuming you want a matte finish). Matte varnish alone can do the job, but will probably not be enough with lots of use or rough storage.
Gloss finish isn't any harder than matte.
Two coats of matte would work just as well as a coat of gloss and matte. If you paint it on, you're probably putting it on thicker than a spray can.