Software, applications, go through different stages of maturity. At early stages (also called "alpha") the applications can very well turn your device into a brick, because at that point, they are little more than technology demostrators. After some iterations, the most dangerous bugs are fixed, and an application reaches a "beta" stage. In this stage, there may be some bugs, but at most they are annoying and will not brick your device. After some more iterations, an app is considered stable and is released to the public. Applications in alpha stages, due to the complexity of their code (and an emulator, or boot screen changer, are complex) tend to have difficult instalations steps and are unstable, leading to unforeseen consequences. That kind of applications are in special repositories, for example, extras-devel, and extra steps are taken to avoid users, that do not have the necessary advanced knowledge to handle them, to install them and brick their devices. Applications in late beta stages and in release stages are in Extras, and ready to be downloaded and used without major hassle.