I am thrilled with Uber in Chicago ... more reliable than taxis in my home neighborhood, generally much cheaper ride to the airport, convenience of payment (automatic from your credit card), clear receipts, etc.
But a couple of things will determine how useful it is to you in Maui.
First, availability - how many cars are out there, and where are they? Given the distances and traffic, it may take a long time for the car to get to you, and there may be more taxis near resorts, etc. That may be the biggest problem at the moment.
Second, the surge pricing. If there is a period of, for example, lots of demand on Saturday and Sunday evenings for rides to the airport to catch the red-eyes back to California, Uber may increase charges, trying to stimulate as many of its drivers to get out on the road. When you "call" for a car, they will notify you that surge pricing is in effect, and include it in your fare estimate.
If you need reliability and will be going driving distances a lot, rent a car. If you just need an occasion jaunt to the grocery store, Uber may be fine, along with reserving a ride in advance back to the airport.