We stayed at Pop and used Uber to go to our Kona breakfast ADR at the Poly on our last day. So much easier than switching buses! I wish we'd have tried Uber sooner in our trip for resort ADRs. It's definitely nicer for going between resorts.
The only thing you have to watch out for is their surge pricing. But that shouldn't be in effect during most meal hours -- usually only in the evening after fireworks shows, in my experience.