Bonjour!
1. They are 15,516 cameras in the London tube network.
2. On average Londoners are caught 13 times an hour on CCTV while in the tube network. While they are caught on average 300 times a day while in the streets.
3. Someone may feel oppressed while in the Borough of Wandsworth because they are constantly being watched by cameras.
4. I think the advantage of this is mainly regarding safety. If your are constantly being filmed while in the metro its means most crimes are caught on tape; which is a huge advantage. The drawback would be that since you are constantly being watched you may feel uncomfortable. As if you had no privacy.
Bonne journée.