Thank you Magzy, I know more less how it works, I just wanted to know if it is reliable and if other users are happy with it, for what I have read on other places it is tough as nails, a bit heavy but good for the money.
For the moment I decided not to use it (may be I add it latter) because two reasons, price and simplicity.
I am going to install just 3 plates on the vehicle, and will see how it goes.
There is a small bicicle shop nearby and I pop in there for ideas and help, they guy on charge, an Argentinean, has been very helpful and with his help we have more lees fixed up all the chain, gears, pedal and other staff, and he will be helping me to make it run properly. May be it will be more expensive than buy it throw internet but the help of a professional is priceless.
however if you're going to be running at 72v (which will be ~50kph?) then you need to make sure you can use the nuvinci it at such a high speed - without pedaling air.
You are right at taht speed I will be not pedaling
I do not know the maximum speed I will be getting with 20" wheels and 72V but should be around that.
Anyway most of the area were it is going to be driven is limited to 30-40 Km/h and plenty of traffic lights and crosses so there will be little high speed...