Files in the National Archives on the Sten here. There isn't much that indicates any kind of official concern about the Sten. Interesting files look to be: WO 291/476 Comparison of rifle, bren and sten guns (1944) WO 233/34 Replacement of the Sten gun by a machine carbine in airborne units: minutes of meetings, specifications and connected correspondence (1943 Oct.-1944 Dec.) DSIR 27/41/ID4 Time-displacement relations of the Sten gun. By A.G. Tarrant (Nov. 1941) AVIA 22/1616 Sten gun improvements. Brig. G. Temple, Major R.V. Shepherd and H.J. Turpin (1941-1947) A couple of oddly-titled ones (20mm Sten?): DSIR 27/41/ID10 Motion study of No. 2 Sten 20 mm. gun. By A.G. Tarrant (Jan. 1942) DSIR 27/44/MAP27 Suggestion for the design of a variable rate device for the Sten 20 mm. gun. By A.G. Tarrant (Feb. 1942) Could the "Sten" in the last two be referring to Polstens? Anyway, the first file WO 291/476 is an Operational Research paper, so that is probably the best bet for finding an objective contemporary assessment of the weapon.