The caption in full is...
An American-built Bell P-39 Airacobra in VVS service. When Lend-Lease shipments of Airacobras to the USSR commenced, RAF fighter pilots dismissed the heavy fighter as a "widowmaker" and simply refused to fly it against the Luftwaffe fighters. "Suited for wide, low, and slow circles," was a comment bestowed upon the P-39 by USAAF pilots. The Airacobra had its baptism of fire on the Eastern Front with 19 GIAP, which received 16 of the type - together with 10 P-40 Kittyhawks - in late April 1942. Although the only available instructions were in English, the assembly of the aircraft and training of pilots were carried out rapidly. The first combat involving Airacobras in VVS service took place on May 15 1942, without loss to either side. Next day, the first loss was suffered when the Airacobra with serial number AH660 was shot down in combat with JG 5 BF109's. The pilot - Starshiy Leytenant Ivan Gaydayenko - survived unhurt.
I see no reason to disbelieve Bergstrom or Mikhailov here and they don't really go into rating the aircraft much.
I have yet to read anything about the P-39 in volume 3 of BC/RS. Perhaps, there is more info in that volume. More likely we'll see more info in later volumes, which will deal from '43 onwards.
There may not have been any "mutiny" from 601 sqn, But there's a reason they only carried out one operation with the type and there must have been very solid reasons for the RAF to deem the P-39 unusable in 1941. I've read on other forums too that USAF pilots in the Pacific joking say that they would have preferred to fly trucks, as they had "better speed and a higher service ceiling". God knows where that came from though.