the fully protected NCBis handy if you are unfortunate enough to have an accident. It's grand to say that you won't, but you might be unlucky. I think that the extra €25/30 is worthwhile.
I accept that you might not be able to move to another insurer, but at least you are not paying the higher premium. If you consider that on a 50% NCB, your normal premium is halved and you only pay 50%. If you loose your NCB, you pay 100%, a doubling of the previous year.
protected NCB seems cheap to me