Ricky Grover has had his voice (badly) dubbed. He sounds like someone from a Bruce Lee film. You can hear his real voice in the British TV show Black Books.
Although the film is set in a fairly generic American urban setting, in the scenes in a moving car in which Sorter (Mark Strong) talks about missing his shots, the actual scenery outside the car windows is that seen from a car heading east on Harcourt Road, Central District, in Hong Kong. At about 13:58 for instance we see the Bank of America Tower's Chinese and English signage very clearly in the background, a few seconds later we see I.M. Pei's Bank of China building behind Strong, and just after that the very distinctive shape of the two towers of what was originally Bond (now Lippo) Centre.
When Sorter shoots the last guy out the window he has a clip in his gun that 3-4" longer than the butt of the gun but when he immediately puts the gun into his waistband after shooting the last guy the clip does not extend beyond the butt of the gun.
When Sorter shoots Paul, the slide on the gun retracts which would mean the magazine is empty. However in the next shot the gun is shown with the slide in the closed position even though Sorter never reloaded the gun