need to add add user names to the post for later retrieval or removal

I’m working on an unique feature, that requires that I add usernames to specific post.

In detail, user clicks button and if he is logged in his wp username is saved somewhere together with the post. User can click and remove himself from the list. There can be many users under single post like 200+.

I believe I have two options:

• 1) Create meta_key value pair and use 1 per user.

• 2) Create 1 meta_key with array value that contains all users.

• 3) I was thinking to maybe use comments system, as for that specific post_type I don’t have comments at all. So I could just attach myself to that system, and instead of saving all comment data I would just store the username.

What do you think? Is there a better way?