It's works as a fairly okay sprite maker and is good for practicing pixel artwork, but there are a few downsides to it.
It's not exactly possible to save or hold onto a work in progress outside of leaving the app open or leaving it in the background for a short time. While saving the sprites as JPG's is neat, helps keep track of previous work, it doesn't necessarily suffice as a proper save system. Having a 6 color palette is a slight drawback, a larger sort of memory for previously used colors would be nice.
The app has potential and does its job, but is somewhat barebones feature wise.
Additionally, I recommend using a phone compatible Stylus with this app, as the smaller the pixels are the harder it can be to touch them with a finger. And it can be very easy to accidentally tap the reset button and lose work.