It relies on radio changing metadata when ad plays or DJ talks, do that even happen often ?

For automated stations it should happen (nearly) instantly. Most "nicer" radios have RDS[1] built into them and high latency would be confusing to users, so updating it quickly is part of having a nice listener experience.

[1]: https://en.wikipedia.org/wiki/Radio_Data_System

Not sure about rest of world, but in the US adverts often play at much louder volumes than the content being enjoyed.