I've been playing with the new Components feature in PowerApps, and I like it a lot so far. It's saved me a bunch of time repeating code between screens.
I've recently used it to create a re-usable loading dialog for when the app is doing work in the background, and my only gripe with it is that the Reorder button is greyed out when selected (This allows you to determine what controls are in-front or behind each other).
When I insert a component into an existing screen, it always places it at the very back. Since the Reorder button greys out when you select it, you need to re-order every other item on the screen to bring it to the front.
In an app where screens already have a lot of controls on the screen, this gets very tedious.