Dark Ages in the British Isles were a fascinating, dismal time of constant wars, in which people fought for survival. A dark age with a deep blend of cultures. The 6th and 7th centuries were a time when invaders (Saxons, Angles and Jutes) tried hard to forge their destiny in a new world with the steel of their swords, shields and spears. The ancient peoples tried to resist, while they saw their kingdoms defeated and conquered by the “barbarians”, and sorrowfully saw how their beloved world slowly disappeared off the face of the earth. But other people must not be left unmentioned, like the Picts, who have always inspired great interest. Or to the west, another island as complex as Britain: Ireland in which many people were fighting for a piece of land, their clans, livestock and supremacy. In short, it is a world we know little about, yet a magnet for history lovers: a time of war and great deeds, where few kings (almost none) died in their beds.
There's a difference between when a game is challenging and when it's so frustrating that it's unplayable. This, I'm afraid, is the latter. Granted, this is a wonderful concept and wonderful execution thereof, but this suffers from something I've seen a lot in mods that would be better than the vanilla, and that's the ridiculous amount of difficulty that, like a particularly bloodthirsty bully, allows you to think you'll come anywhere near enjoying yourself just so he can take everything you own and traumatize you more deeply. "Oh, look at your wonderful little army you spent the first few hours of the game working on," it says, "Let's see what happens when I throw a random group of bandits at it with three times the manpower." One needlessly complicated and ungodly frustrating fight scene later, your precious army with which you would convert the world to the love of Jesus Christ lies dead on the ground. MAYBE this is more realistic, and MAYBE the mod has wonderful features (everything about it, really, especially the naval batlles), but when it gets to this point, realism should be sacrificed just a bit and all those wonderful features will never see the light of day since you can't walk two steps outside a city before you're up to your neck in the corpses of everyone you love.
Bottom line: Recommended with extreme caution.