if the tens of dollars is ok, if you enjoy breaking up your journey, if your bladder like mine cannot wait for the next toilet break, then yup flight + grab or coach is great!
Time taken is almost similar. but if you push it like check in 60min prior, flight on time, immigration clearance only 3 4 cats, grab on time, you can save up to 2 hours. But all the stars must aligned. hahaha
if travelling with partner and not a lot of luggage, can take normal grab although be prepared they wont take you after knowing you are going up mountain. I suggest spend that extra 10rm or so and opt for grab plus. If extremely lucky, go for grab premium, you may just get 100ish rm for a 6-seater alphard.