http://www.nabendynamo.de/produkte/pdf/Ueberspannung.pdf

This document states that you should add an external device to the circuit on you bicycle to limit the voltage of the dynamo. From my point of view it would make no sense to use a voltage limiter inside the dynamo because it would try to limit the voltage even if the lights are completly switched off. This would draw a lot of power from the dynamo just to burn it in the limiter... Nobody wants this ;-)

The only practical solution is to put the limiter behind the light switch and therefore it is normally located in the front reflector.

To cut a long story short: You shouldn't experience any problems with the SON, I think, without warranty of course!