With any invasive procedure (such as needling) infection, bleeding, bruising, lack of improvement, and worsening of existing scarring are risks.
Several treatments are required with the needling method to see improvement, but how much improvement you'll get depends completely on the type and severity of your scarring. Needling may not be your best or only answer.
Acne scarring is one of the most challenging problems to improve, but it can be improved. Improvement, rather than erasure of scars, is the only realistic goal. There is no one best method for acne scarring. Often many different methods are required in combination to improve acne scarring, depending on the type and location of scarring (boxcar, ice-pick, rolling, etc.).
Surgery, dermabrasion, punch grafts, subcision, laser treatment, TCA CROSS, and needling are all methods that can work, but it's important to find a physician with considerable treatment experience with acne scarring. Beware any physician who only has one tool or one answer... you will likely need a combination of treatments for maximum improvement.