Wow, that's a helluva deal considering it's 4 bucks.. How often do they have these sales? And more importantly, would I be able to keep the functions of my phone, such as S voice and Google search?
All your apps will remain in place and in full use. The launcher just changes the application dock at the bottom of your homescreen and gives you much more customizing options for your homescreen(s). Also gives some other options in the application list too depending on the launcher.
Some launchers react differently than others with devices, so give a few a test drive and see what you like. Nova launcher is probably one of the best.
One feature you will probably love about 3rd party launchers is they have a backup and restore option to save your settings and setup of your launcher dock, homescreens, etc.. Great feature.
Much more to talk about with 3rd party launchers but its easier to just grab a one and check it out for yourself.
Good luck and enjoy!