Seems to be a very slow mirror of the Panzer Tracts site.
The main site (which loads immediately) is at:
Panzer Tracts Home Page

Tom Jentz & Hilary Doyle are at the pinnacle of research into German armour, mostly technically directed but also exceptionally expert on it's usage.
The 'Panzer Tracts' are each excellent, brief, and well illustrated summarys of their subject based only on what can be proven as 'fact'. It's always interesting how many respected panzer websites are based largely on material lifted verbatim from their pages.
What I would say is be
very sure your interest in a particular vehicle is strong enough to warrant any purchase, they're far from cheap for slim volumes with rather austere production values.
Cheers,
Adam.