Hair fibre like Toppik or Caboki? I did after I started topical minoxidil and before finasteride.
I had diffuse hair loss so it helped give the illusion my hair was more full. You saw less scalp. I usually put it on after I finish styling. Then I put hairspray to set everything.
As I lost more hair, though, it became harder and harder to cover things up. The best way to use fibre is if you have some hair and the fibre just sits in between the surviving hairs on the scalp or it clings on to some hair. If you don't have hair in that area it's very hard to get a natural effect. Ignore all the photographs of the people who have a bald crown because in order to achieve that effect you need to sprinkle 1/5 of a bottle on it and it won't look 3D because the fibre is only so long.
Since I used finasteride for a few years I find myself using less and less because my hair grew back in. I sometimes forget now and just go out. I have a side part so I can just move my part a little bit to cover it up or not style upwards so aggressively.
For you - why would you use it? It won't fill in receding corners. You said your whole hairline is receding slowly. It will help if someone looked at you and you styled your hair up or they look down on your head from above and you're thinning. You can use it to cover it up. Are you losing hair that way though?
A few things about fibre: It's lightweight. Don't let women brush their hand through your hair. In fact when you use it for a few years you will just instinctively move your head away from people touching it. They'll get the fibre on them. If you hairsprayed it down you can have someone pat you on the head but if they start running fingers through it chances their hands will pick it up. If you are applying too much, you need use a dry towel and brush your forehead. Sometimes it will fall there when applying and you look like a homeless person.
You will also develop natural instincts not to jump into water and swim. You will also have natural instincts to run and hide when there's a rainstorm. With hairspray, some light drizzle is okay but too much will basically run the fibre out of your hair making your sparse areas even more sparse. Worst case people see streaks of fibre coming down your face. If you do get stuck in a rain storm the best thing to do is not touch your hair and just let it dry naturally.
Too much fibre or not using hairspray after fibre to set it also creates issues on pillow cases. You will also wear a cap when you go to the dentist or you get a facial or massage or anywhere where your head might rest on an area. I once had a hygienist who had to change her ...apron?...because she was vigorously massaging my hair and face with her breast when doing hand scaling.
Finally you'll probably need a cloth to wipe down your sink after styling your hair. Chances are things that look like residue from an electric shaver will accumulate. I used Toppik in the beginning but the dark colours turn green after it stays on your hair past 24 hours. It's not a problem for me anymore since I work out every day so I rinse or wash my hair every day and I just reapply everything after. I switched to Caboki because of that.
Lou Avery from Mad Men Season 7..so around 2014-2015
Same actor in 2014
For sure the TV show people used fibre for him as a concealer. Obviously blow dry to give it more volume and instead of foolishly trying to comb everything straight up try to have a bit of a comb over.