Looking at the download links, I do see Android versions there, but I’m not sure what they’re like (or how easy they are to use), as I only ever used the Windows version. For windows, it’s as simple downloading the file, extracting the zip, and running the executable (they’re in portable form, so there’s no installation needed; for windows, at least). Here’s the link to the download page: Index of /ci-builds/graphics/krita/master
(EDIT) - Forgot your safety concerns. I’ve used versions of the Nightly Next almost primarily for years. Apart from occasional stability issues (because they’re works in progress), I haven’t had any issues. I do recommend you back up your Krita folder though (the one that holds all your folders for resources and all of that), just in case.