Forgive me if I'm wrong or massively generalising but from what i undertand, the British dumped their Airacobras first chance they got while the USAAF pilots don't seem to have anything positive to say about the P39. On the other hand the Russians loved the P39.
Why such different reactions to the same airplane?
I touch on this in this thread a little as part of a larger post, so might be of interest. In short, it was terrible at high altitude, the preferred engagement level in the West, but much better going low and slow, which was more common in the east.