Most of the range is very old – originally Asgard from the early 1980s but there are some recent new additions to the range of Landsknects.
They mix very well with the slightly earlier Minifigs but are generally a bit more dynamically posed and sculpted with more relief. They mix well with at least some Essex infantry bit the Essex horses are much bigger. I've not made a direct comparison with Donington but I think they vary a lot anyway.
Generally I think you can mix infantry figures with different heights and builds as long as you replace the weapons so they match – that's the approach I've followed with my Italian Wars French and Late Romans, both using a mix of Alternative Armies, Minifgs and others. It is easy enough to do this with pikes and spears – a bit more time consuming with crossbows!
Here, for example, are a mix of crossbowmen:
TMP link
From left to right: Alternative Armies/Asgard, Gladiator, Naismith, Naismith, Essex, 4 from Old Glory, 2 from Venexia
Despite having used a lot of these figures and liking them, if I hadn't already had them in the lead pile (many dating back to the 80s!) but was buying new, I would have looked at more modern ranges with multiple poses for each type..
smallitalianwars.blogspot.com