Myself have never used one. I haven't had that problem with the S-40. Now when I had my Rebel, that was a problem I ran into alot.
Guys used to talk about these light changers on the Rebel forum. Some said they worked great.
Like the person above me mentioned, the sensor for the lights are usually
visible by looking at the pavement.
You have to be kind of centered in the space. Well at least that is how I find it works for me.
If you don't want to run the light, take a right if possible and come back thru the light from a different direction.
kim