I make loneoceans gfs16 MOSFET tailswitch in the past for my S2 flashlight and it is working good! The benifet is that the switch fit entirely inside flashlight.
Here is loneoceans thread: GFS16 - Battery Indicator Tailcap Light & 1mR FET Tailswitch! (Rev B)
Here is my project: >> Homemade Gxb172 led driver (complete!)