I have been developing iOS apps since I was in the 7th grade. Since then I have worked on numerous other projects, including ones in team based environments.
Native apps run the fastest and are the most reliable. This is why I build all of my apps using Apple's own Xcode software with either Objective-C or Swift.
Well designed apps make people more inclined to return. It also improves brand reputation.
Slow apps are one of the main factors that drive users away. I recognize this and strive to make every application I build as fast as possible.