Im not on duta, but I always take fina on cycle, off cycle I take it from time to time. Protocol is 1mg ed together with nizoral.
From my experience fina has no bad effects, hair is a bit stronger while on cycle and i get less acne as well. Also I think libido is higher when i'm on fina.
Top of my head has very thin hair and not much hair, it has been like this since mid twenties, slowly but steady decrease in hair. While on fina it gets stronger.
But im a medical study of 1, so not very reliable, just my experience.
So, here is a good medical case on duta that actually has some evidence that free test is higher while on duta and exogenous test:
Muscle Mass Gain From Testosterone Not Affected by 5α-Reductase Inhibitor