I couldn't resist and bought the upgrade yesterday. Now that i'm playing with it my very first impression is that, out of the box, i definitely prefer the somewhat raw and organic sound of Albion Legacy. But i can sense right away that with Albion One it'll be much easier for me to sketch new ideas and write full compositions. To me, the magic comes when i layer both One and Legacy patches where it's appropriate.
One has a rather light and quite compressed sound to it, which is really easy on the ears. That's great for me when i want to try things out or just write without getting overly concerned about the sound itself. But Legacy, on the other hand, has such a rich and full sound, which is what made Spitfire such a unique developer in the first place, in my opinion. Albion One doesn't quite have that. So i'm more than thankful that Spitfire decided to keep the Legacy content for us to use, because that's where the library really shines now. I'll write with One for the most part now, as it's incredibly easy to use, sounds great and is just a joy to work with all around. But in mixing stage, where i'm trying to find the right and ideal tone for the whole piece, i'll definitely keep using Legacy a lot. I'll layer them wherever possible to get the best of both worlds.
To me Albion Legacy wasn't always exactly easy to mix, as great as it sounds. I feel that One will be much more convienent in that regard. So i think they accompany each other very well instead of one replacing the other. Have in mind that's my very first impression of it after trying it out for myself. But it confirms what i assumed from the demos, reviews and what i've read on forums like this.