Unimog Club UK

The way I read it is a tractor not capable of 25mph only has to use one, on a unrestricted dual carriageway, by that I would say a unimog wont need one.
Personally I would still use one, the traffic could still have a 30mph speed difference even when traveling at 40 in unimog.
With most tractors unless I was in a built up area I would think about putting the beacon on, hoping to warn people some thing a bit larger than a car is coming, and as you say when working.