Derma rolling doesn't do anything but hurt.
What really works is vitamin c powder mixed with pure glycerin as a mask or mix a pinch with your moisturizer. Mandelic acid works great and so does lactic acid. If you can find a toner with those two acids in it you're set.
I've also found jessners peels to be very effective in treating acne, hyperpigmentation and shallow acne scars.
I bought an .5 mm roller and used it for 3 months 1-3 times per week. Sometimes it worked for better topical absorption but it was just a pain to roll!
I'd say since you bought it use it! You might like it but peels really do work the best for the left over marks from acne. Depending on the severity, if yours are very light you could probably fix them with an aha cream/gel or lotion. If the hyperpigmentation is pretty dark I'd say a jessners peel would work.