Didn't do me any harm
although I only took 4 before I started my PPL. I would have liked to have completed all of them except RT, but ran out of time before my full-time course started.
If someone wants to do the exams first, why not? Yes, some parts were harder to understand but not impossible; sloping runways in HF &PP didn't make sense (still doesn't as I don't use 'em
).
Jonathan, the answers to your questions are both "yes".
Cheers
Whirls