Honestly, a lot of stuff like this is greatly dependent on placebo effect. My girlfriend is SUPER sensitive to the placebo effect, and if she believes it will work? It doesn't matter how "quack-y" it sounds, it'll work. If she believes it won't? No number of studies talking about the success rate will make it work. For me, I have an anti-placebo effect, so when something does work, I'm surprised.
The power of the human mind is really amazing. If you go into it believing it will help, then you have a decent chance of seeing it make a difference. If you go into it with a lot of skepticism, though, it's probably not going to help much.
And like someone else said, it's not going to have the effects of HRT or anything like that. At best, it may help with your mental state and feeling more feminine, which can be really important just on its own. There's no harm in giving it a try and seeing if it helps, especially if it's free YouTube videos (I would avoid anything that costs money, personally; a lot of that stuff tends to be scams).