The Osprey books are great for iconography, you can show your players the plate to give them a feel for the period you're aiming to play.
When I first started roleplaying, I was mastering Légendes de la Table Ronde. It was supposed to be sixth century Britain, but the fashion and technological level was Chrétien de Troyes twelfth century between Champagne and Flanders. I would have liked to have the corresponding Osprey book at that point.
The campaign we're currently playing is set in the ninth centry, mail shirts are rarer, fighting on horseback is rarer. The Osprey title Anglo-Saxon Thegn helps me setting the tone. The players understand that there won't be plate armours.
One thing I only learned recently is that Osprey has a gaming arm, Osprey Games, with board games, wargames, and roleplaying games. I was under the impression that only miniature wargames would be arrayed there, but the selection is wide enough.
Those Osprey book shine not just for their plates. They feature texts that are not too short, not too long but rich in learning. Here are a few lines that talked to me as a gamer:
Most treatment took the form of traditional cures and charms passed on by word of mouth from generation to generation. The line in the Riddle of the Shield — makes it clear that herbal poultices at least were in use.
It has been said that Anglo-Saxon medical expertise was concentrated in the hands of the clergy; this in large part assumes that clerics would have been the only persons able to read or copy written medical texts. All that survives of these texts is a small number of Anglo-Saxon leech books which contain herbal remedies and semi-magical poetic charms.
The Nine-Herbs Charm for example involves a concoction made from a selection of plants including feverfew and nettle, which is to be administered together with the following rhyme:
If you were a skin-shot, or if you were a flesh-shot,
Or if you were a blood-shot, or if you were a bone-shot,
Or if you were a body-shot, as never before in your life.
Some ailments for which cures are given in the leech books are compared to war-wounds. The ylfa gescot or "elf-shot" is a pain caused by invisible attackers from the supernatural world. The waelsperu or "spear of woe" is an acute pain caused by a wound from a seax forged by the "six smiths of Satan". It may be that some of the corresponding cures had originally been intended for battle injuries. Little is known of the effectiveness of these primitive remedies, though it is likely that few had anything more than a placebo effect. Recovery from battlefield wounds in an age when knowledge of medical hygiene was minimal must have been largely a matter of luck.
That made me pause, and think about medevac in Wolves of God. It could be summarized as "cart the man to the nearest minster, hopefully one were you already have connections with the abbot and where there is a skilled healer".
I have the impression that they don't update those books, they simply reprint them. New content taking into account recent archeological work seems to show up in newer books in newer series.