I think it depends on instructor and your own level of skill and confidence. I had two different instructors for mine and learned a lot with one, but not with the other. It was a useful experience because at the time I had only about 15 dives and very little confidence under water. It was good to do the deep dive with an excellent instructor, as I was very nervous about it, but found it wasn't a problem. It was also good to experience night diving under supervision, especially as I got disoriented, but at least there was someone to help. I think ppb would be good with a good instructor, but my instructor for that bit wasn't great.