Bottom line is get a flex shaft if you can. It is not indespensible
until you get one. It will speed up the sanding in many instances and
it will compliment your graver, bow drill, and polishing machine.
The flex needs learning same as any other tool. It’s not always
better than hand methods but with practise it is faster, requires
carefull control, and mistakes can be more drastic!
A micro-motor is happier at high speed and lacks torque at low speed,
enough difference from a flex shaft to need it’s own learning.
I use all three. Flex shaft for heavy cutting, micro motor for high
speed finess, and hand power for ultimate control. Sanding sticks are
best for flat planes or surfaces.