That's because it uses BoB footage.
And also a liberal dose of CGI.
It's a Czech movie, so it's free from the trimmings of Hollywood. But still, expect something more like Pearl Harbor than Battle Of Britain, in that it contains the usual love triangle sub-plot. But that is as far as the comparison goes. Beyond that, IMHO, this is another example of a foreign movie showing Hollywood how it should be done.
BUT... it is plot heavy and war light (if you've seen the trailer then you've seen most of the flying sequences). I had to watch it twice to get my head around the character development and plot subtleties that I missed first time around. Still, I enjoyed it and bought the DVD.