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.
For whatever reason, when we've gone into the ultra power saving mode on the Galaxy S5, coming back out of it has removed all customizations we've made to the launcher. All that has been left is the Phone app and a Google folder containing three app shortcuts. So if ultra power saving is something you're going to be using a lot, take note. And remember that the Google Now Launcher isn't officially supposed to be on the Galaxy S5 right now.
That said, everything else seems to be working just fine. If you've already sideloaded it and have noticed any other quirks, be sure to drop them into the comments below.