I'm really curious about this as well. The old Purity Seal is garbage, so
tbh there's a lot of room for improvement.
I've struggled to find any good reviews of the Munitorum Varnish, and the majority of search results are online shops, with no customer reviews. I've found this though:
https://www.reddit.com/r/Warhammer40k/comments/7hgdw5/do_you_varnish/
So it seems the M. Varnish has a satin gloss, and as I would have preferred a matte look, I think I'll continue to use Vallejo.