When using MMing with PR, s/r and dip first until you've gained enough familiarity with the material to think it's beginning to gel. Then use MM to organise your thoughts. Used in this way, the MM helps you to see what's missing and what's not and helps gelling.
Another way to use it with formulae would be to just use it to list them. In math class, we used to do this. My teacher used to implement "three wonderful minutes". You were given 3 mins to completely redraw your mindmap from memory. Quite a useful tool after awhile, particularly since this forces you through the recall process and involves soom muscle memory.
If you find that MMing is tedious and time-consuming, you're probably trying to force too much information onto it. It's for linking ideas, not copying books. I'm just guessing here, but I often commit that "crime" myself. For things like derivations, a separate note-taking would probably be appropriate.
When teaching, I sometimes use idea mapping rather than mind-mapping. This one can probably be classified as a version of MMing, but I like to think that I developed it.
It's great for showing flows of ideas, which I find MMing cannot do. Tell me if you're interested in this and I'll try to get a description up.
Good luck! 
KWLee
