@Diving Dubai is absolutely correct. And I worded things badly.
A well run DM course can be about the most productive thing a recreational diver can do. There are lots of elements you need to complete. And if you have a decent mentor you will find out where you are not so strong and with guidance improve.
There are many curve balls thrown into the course like having to swap kit under water. And if you combine all those things with regular diving and observing/assisting on courses then you will both enjoy it and learn from it.
I can second this whole heartily. One of my friends just loves to remind me that I was dismissive of the DM course (that she was thinking of doing), and at the time I had't bothered with. I held the view, like so many that it was an easy course and you would learn nothing as a diver, as it was aimed more at those wishing to become instructors.
How wrong I was.
Bear in mind also that I already held a Dive Leader qual - the BSAC equivalent, and I was certified for Adv deco and could hold stops in trim with a good degree of accuracy (less than 1@ total vertical movement on a blue water stop.
While some of the sections were a breeze, others weren't. On theory I re learnt all my tables and learnt from scratch the ERDPml (which wasn't around when I took OW), not just so I could use them but so I could explain and teach.
My swim tests (800m and 400M) were difficult, I hate swimming - it wasn't' a physical limitation just a mental one. I learnt to get on and deal with it.
The biggest learning came from the skills demonstrations. Not only re learning skills I'd long ago forgotten, but from being able to carry them out slowly and clearly while neutral. I came down to earth with a bump and bruise my personal ego when I found that holding a stop in blue water is a breeze compare with being seemingly motionless in a shallow pool, where if your breathing wasn't' precise you were either on the surface or the pool bottom.
I became a more considerate, patient and tolerant diver (according to my wife) certainly had to take more care, not just to be sen as a role model, but because as a DM or Instructor, no-one buddy checks you, and we're all human and fallible, and often distracted helping others
I discovered the challenge of guiding less experienced divers, where you need to keep them together, not go too fast nor slow, monitor their gas - and keep that picture in your head, gain more situational awareness, e more aware of changing conditions (with with experienced divers is easy you can just push through current etc, not so with novice, where you're trying to get the most dive time from their gas consumption.
But as
@HantsDiver stated, it's all about the people that mentor you and challenge you. A DM course shouldn't be a race to complete ASAP, rather a journey to experience and learn as much as you can from.
That friend above? She took her DM (in Mozambique) had a fab time, but the biggest compliment is that she always requests to be my CA when shes' around and I'm teaching. Apparently I challenge her, mentor her and help her develop professionally while she decides if she wants to become an instructor and tech diver
Who would have thought that 2 years ago? Not me