They have given the contract for toll plaza to different companies which has made matters worse. Now your e-tag won't work on M1 which requires an M-tag. And the M-tag won't work on M2. Add to that several exits on the M1 have the m-tag booths out of order most of the time.
A person going from Peshawar to Lahore has to stand in the queue at M1 exit and waste a good half hour before lining up for the M2 entrance and wasting more time there. They should have made this toll booth on a side/link road only for those exiting at Islamabad. Or at least, not under a flyover so it could be expanded to more booths.