Thank you for your comment, I don’t think the simultaneous action over the same row by different user on this case won’t be an issue, because of
Each user is targeting the value of own useremail address text value in the field. If not exist, then add by action, else delete by action as well. Even if the action is triggered at the same time (in the mil sec world, i dont think it will happen though…), it is nothing to do with action made by other user which is taking care of their own value (email address)
Counting the number LIKEIT sounds good. I will alter my sample accordingly.