Have you ever been working on a project and ran "yarn install pkg" only to realize that the project you are working on doesn't use yarn so now you have to delete the yarn lock file and re-run the command with npm? Welcome to the future!! Just use "nstl" and you don't have to care about which package manager to use, or which arguments to use. Is it --save-dev or --dev? No one cares. use whichever one you want.