I have used a Snap-On flex head torque wrench since the late 80's. The flex in the head is minimal on mine and has never posed a problem. I know the flex head has allowed me to get into several spots without finding another length adapter. I guess it depends on how much flex the torque wrench allows. Too much flex will change the torque values. If memory serves me, the flex on my wrench is 15 degrees or less in either direction.
