No dipstick is surely sub-optimal but not critical as the vehicle will have some sort of level indicator. That said, how much one trusts the indicator over time is another question, but you know the capacity, know (roughly) how much you drained and how much you added. Just did oil on the new 911; looked like ~2 gallons were in the drain pan, filled with 8 qts. and topped off per the instructions using the gauge. Easy...