I just purchased four new Trustfire 16340s (CR123) labeled 880mAH from EBay vendor toymodel55. I tested them at 300mA and 120mA discharge rates, from 4.20V to 2.70V. Results are 471, 472, 485, and 507mAH at 120mA, and just slightly lower at 300mA. I have not tested the claimed internal protection circuit.
So, the short answer is that they work, but well below the claimed capacity.