The main issue would be that most of the traffic is in one direction, esp. on the way "back"; that is, in the a.m., people are headed toward Hana, and in the p.m., going back to the major tourist locales.
Given that there are many places where the traffic is one lane only, it could be irksome to buck traffic; however, if you spend most of the day seeing the sights, by the time you get to Hana and on the road "home," you will be joining the throngs!
Might be a good way to go, if you want to hit the O'heo Gulch Park (7 sacred) pools for a morning visit first, before through Hana, and seeing all the other sights along the route.