Thought I'd update as it might be of interest to other who struggled on fin.
As I've already posted, fin caused me brainfog from the get go. It was horrible, basically hit an hour or 2 after taking it and persisted most of the day. For those that say it's all in your head I experimented with puting a 1/8th of fin inside a vit d capsule, the chose between one with and without fin, at the end of the day I'd check which one I'd taken. It was very easy to tell when I had taken the fin. Also had a couple if days I felt great, only to find when I got home I'd left my bit of fin tablet on my desk and had forgotten to take it.
However I persisted and about 3 months ago started noticing my daily brain fog was not as bad.
I started taking 1/8th of 1 mg everyday as opposed to 5 times a week. About a month ago I started taking 1/6ths and in the last week I'm taking 1/4mg some days. Brain fog has been minimal with this higher dose. 1/8th now causes basically no problems.
I'm going to try and work up to 1/4mg most days.
Morning wood was another problem, it disappeared when I started fin. However in the last few months I've had a few days here and there when I woke with a solid MW.
Apart from this I've no other problems.
Hair is looking really healthy although it hasn't thickened, it isn't staw like anymore. So at the moment I'm happy.
I'm not sure if it took time for my body to adjust but I'm glad I kept going.
TLDR
started fin on low dose 11 months ago, had horrible brain fog but over time symptoms subsided and have been able to increase dose without major sides.