I use this app a lot. Very practical and intuitive. Great for saving well documented calculations templates that I can use later to solve problems just by changing the variables and saving under an appropriate name. Aside for a few needed aestetic touches here and there, everyone can find very practical uses for it and enjoy the benefit of the companion app for iPhones & iPads that work very well through iCloud.
But since the last app update (I’m on a MacBook Pro mid 2012 running El Capitan), the app often hangs at launch and when clicked on again launches two windows. It also crashes frequently during use. Finally, every time I quit the app, an Apple report window pops up informing me that the app has crashed.
While I can work around the bugs in this software (I’m a developer), I trust these issues will be resolved in an upcoming update (hopefully soon).