Largely all is well, until you enter ultra power saving mode
Here's a quick word of caution to anyone sideloading the Google Now Launcher onto their new Samsung Galaxy S5. Largely Google's own KitKat launcher works faultlessly on Samsung's latest Android handset. It's smooth, it's snappy, and it's a great option even if the Galaxy S5 isn't officially supported. But you do run into some issues when you switch in and out of ultra power saving mode.