How good is dermabrasion for acne scars?

Very good.: Dermabrasion can be very effective in improving the appearance of acne scars, although it may need to be repeated.

Often very good: Mechanical dermabrasion (not microdermabrasion) can provide a "plane" removal of the acne scar edges, smoothing and flattening of the scar depressions. Better on scars that are crater-like (pox scar example) than deep "pit" type scars (called ice pick types). May require more than a single treatment, as there are limits to depth. New skin from oil & sweat glands and hair follicle to resurface.

Depends : It really depends on the type off scar; it does not work well for atrophic scars. Fat transfer may enhance results as well.