How satisfied are people with hair loss treatments?

I experienced hair loss once when I was young, so I'm very interested in this kind of hair loss treatment. However, hearing that they inject directly into the hair follicles... makes me a bit scared.
I wonder if it will hurt. A needle in the head... I have a feeling it might be painful. I've been thinking simply about it, but I'm curious if hair loss treatments stimulate the hair follicles to actually help hair grow back. I'm also curious about the satisfaction levels of those who have received the treatment. But there are so many types of hair loss, you know. I'm wondering if the treatment methods vary depending on the type of hair loss. I'm also curious if there are any side effects. I assume a single treatment won't be enough, right? What is the most popular procedure? For me, the most important thing is that it doesn't hurt. If I get scared of the procedure, I think I'll end up hesitating.