If the device is lying open on the table, 5m is very good to understand what is being said. If there is a table or a wall in between, then it might be up to 2m to understand the conversations well.

yes, this is absolutely suitable for lectures, but for music the quality is very, very poor.

Without testing, this is difficult to answer. If it is only a question of understanding what is being said and there is not too much background noise, I would say YES.