I finally managed to put MotorMax in the Radiator after draining about 1L or coolant DIY style:
before MotorMax, the engine water needle would get to a stable position in 7 minutes 15 seconds (cold start)
After MotorMax it now takes a mere 6 minutes, indicating the heat is transferred much more quickly. (following day, cold start again, of course)
The water temperature needle seems to sit a little lower than what it used to, I've taken pictures of before and after... you can see them below.
Not too sure it made any difference on fuel consumption to be honest
With regards to overall cooling abilities, it could be just my impression, but the aircon seems to be working better, especially these days that I really needed it on full blast!.
Overall, for £25 I think it's a worthwhile addition to your cooling system, wonder what the SC or TT guys would experience with it on!