This is very watchable as a drama but is surprisingly sloppy in historical detail, for instance in the last episode some of the aircraft in the battle of Britain hanger had 'invasion stripes' used for D day four years later. One can easily identify many similar careless mistakes.
For me though ( I have to declare Polish heritage here) the great positive feature of this production is that it is the first British war drama which recognises the immense suffering of the Polish people under German occupation and even touches on the major Soviet contribution to that suffering in eastern Poland
It would be too much to hope for, I guess, for the effects of Nazi and Soviet propaganda to be fully shaken off in respect to the fighting in September and October 1939; The Poles had tanks (more than the British at that time)) and aircraft and inflicted heavy losses on the Germans and these would have been much higher but for the Russian stab in the back which made things totally hopeless. The bicycles/cavalry against tanks tropes are fosillised but still effective Nazi propaganda.