Many thanks for this review, Mark, and for putting us on to this excellent publishing house.
For some reason, I can't make the link you provided work, so I Googled "Bulgariana" and came with exactly the same link, which worked. Go figure.
The aviation books seem to have very high quality graphics. These folks publish an amazing amount of information on military equipment of Bulgaria and Bulgarian history.
I haven't been able to find the Nomanhan book, however.