Finasteride only prevents the reduction from hormones via the 5-AR enzyme. This prevents test from turning into DHT.
Some hormones, like Deca, are actually more likely to cause hairloss before being reduced, so taking Fin actually speeds up hairloss while on Deca.
I dont think anybody knows for sure if it will help or hurt while you are on Superdrol, but I would be safe and NOT take the fin while on SuperDrol.
Why? Because your test levels are going to be in the gutter while on Superdrol - you wont have any DHT floating around. Secondly, if SuperDrol itself causes hairloss, it will be WORSE on fin because it wont be able to become 5-AR reduced.
Instead I would save it for post cycle therapy, when you want your estrogen and DHT to be low in order to kick start your HPTA.