Personally I really enjoyed and valued my PB2. I did it about 10 years ago. So was about 40. But had played around on boats on the river and sailing dinghy's on and off since I was a kid. As a 15 year old I was very skilled at maneuvering through locks in the Thames.
Decided to do my PB2 after buying a 15ft centre console to take to Spain with me on holiday and use on the Solent.
My main reason was to get my ICC for Spain.
PB2 was taken on the Hamble river and Southampton water in winter.
Strong tides and strong winds for the 2 days. Just 2 of us on a rib and the instructor.
The most valuable things I learned.....
Maneuvering in tight spaces. We spent several hours in a finger pontoon mariner, turning a 7.5m rib 180 degrees in a 2 berth finger with a fast tide and winds. Despite being a fair hand at maneuvering, I learned a lot under instruction and just operating in a safe but challenging environment. Especially as it was not my boat that got damaged if I messed up

2nd was basic reading of charts and navigation. Really essential around the Solent. Never really needed on the Thames

3rd was some basic knots.. Just wish I could remember the damn things when I need them.
All in all, for me it was a couple of hundred quid well spent.
Now, if I had done the same on a lake, without the wind and tide I don't believe it would have been half as valuable.