I hated fin, I took it before I ever juiced and it was effectively chemical castration for me. Effective for hair loss though. But I had major sides including limp dick, insomnia, depression. I mean I could still have sex with my gf but orgasms weren't even fun.
On cycle though this shouldn't be an issue, you are keeping your test high artificially and as long as you have an AI you should be good.
For me, when I started my test cycle, my hair got thicker. Weird but welcome.