Tried and tested headsets:
Plantronics: Supraplus SL H351/A (P/N 36828-02) with adapter unit 3,5mm jack plug (P/N 40845-01)
GN: GN 2100 Duo (ord. no. 2139-09-04) with adapter unit 3,5mm jack plug (ord. no. 8800-00-51)
GN: GN 2100 3-in-1 (ord .no. 2126-89-04 with adapter unit 3,5mm jack plug (ord. no. 8800-00-51)
The essential difference between the GN-Headsets is the microphone arm. The Duo headset has a metal one and the 3-in-1 a flexible made of plastic.
All three headsets are quite similar with the speeche quality.