Optical flow without gps


I am flying indoors so no GPS.
Can I use the optical flow sensor to navigate and if yes, how precise this navigation is going to be?

Also I am using APM 2.8, and in the above link the description to connect an APM 2.8 with optical flow is not given. Is it the same as APM 2.5/2.6?

Only ADNS 3080 is supported for APM 2.8 right?