Some guidelines for the comparison of different quantum key distribution ex
periments are proposed. An improved 'plug & play' interferometric system al
lowing fast key exchange is introduced. Self-alignment and compensation of
birefringence remain. Original electronics implementing the BB84 protocol a
nd allowing user-friendly operation is presented. Key creation with 0.1 pho
ton per pulse at a rate of 486 Hz with a 5.4% QBER, corresponding to a net
rate of 210 Hz, over a 23 Km installed cable was performed.