I have it, and it works really well in the rain. Not that you can really tell that it is working since there is no real noticeable effect. It just limits the power so that you barely aren't spinning out of control, it isn't like factory traction systems that work like on/off. So when it is on I do not even notice that it is working for me, full throttle takeoff in rain just feels normal, to convince myself that it does work I try that again with it off and the car winds up pointing into oncoming traffic. It did snow this week but I didn't bother to attempt to get out in the snow since I couldn't get off my lawn since the car would spin out at any throttle. I would imagine it would work in the snow too, but it helps if the car can get moving.
