I am still really enjoying the 6lb nanofil with few problems. The 4lb though is still irritating how difficult it is to get a satisfactory knot you can trust with it.
Taking Paulus' advice I have adopted the doubled blood knot for the leader connection and having very good success with it, even though it is the most painful knot in the world to tie. With the 6lb nano i am regularly busting 10lb Nitlon DFC leaders, with the 4lb nano I can pop 6lb Nitlon DFC leaders once i get a satisfactory leader knot tied.
I will stay with this nanofil until it needs replacement. Might give exceed a run next time around.