If you are spending time developing SimbleeForMobile native UI or Evothings UI, you might find that Blynk
is even more efficient than that. For very simple UI, you can achieve that like it said ~5 mins. It is available free in both Android and IOS. If you need more UI, you need to pay in-app store to do that. And, if you publish your app into app store by paying another price, you can roll into both IOS and Andriod very quickly.
The limitation would only be the UI they provided. If you need very complicated UI, then you would go back to those two that I mentioned. But for very rapid development for a proof of concept, this fits in well.