If you run gravity box and xblast at the same time some things might conflict such as the status bar clock. There might be two of them so just disable one in either app but from personal experience there is no conflict with using both just make sure you don't have two things enabled for the same thing it'll display both and look goofy.
XDA Developers was founded by developers, for developers. It is now a valuable resource for people who want to make the most of their mobile devices, from customizing the look and feel to adding new functionality. Are you a developer? | Terms of Service