Do you want to make a multi-tag system with MongoDB or regular MySQL?

  mongodb, question

I want to make an activity system, each activity has a lot of tag, of course, there are the number of participants, time and place. Recently, I learned mongodb and feel that it is very convenient to use mongo:
meeting table:

{_id: 42, name: "someName", tags: ["chicken", "parrot", "hovercraft"]}

person table:

{_id: "somebody@gmail.com", name:"LiMing", phone:"1381671537"}

person activity table:

{_id:56, person: "somebody@gmail.com", eventid: 42}

Many people will attend every activity. I don’t know if it is better to use mongodb or mySQL, the traditional database, if the system is large, especially if there are more participants.
There is also query efficiency, such as:

db.meeting.find({tags:{$in:["tag2", "tag1"]}});

Is it so high?
The traditional database needs many-to-many tables. I don’t know if the traditional query speed is high or if mongoDB is used directly.
Originally, I wanted to design a table. If there were many people taking part in the activity, such as 200 people in person, would it reduce the efficiency? Sometimes, I am afraid that there will be a problem of locking the number of people to be added and the number of people to be reduced. For example, how many people will be added to a certain activity at the same time?
MongoDB How to Query Multiple Tables join?

Only a little advice:Don’t use techniques you can’t control..

You can use whichever you are familiar with and which you are more proficient with.

If neither has been used, consider MongoDB.