Looks like they made the 25th May after all... just!
Yessir.
I upgraded by way of Kies. It's since downloaded and rebooted. So, it's optimizing apps at the moment. Kies told me to disconnect and reconnect the cable but I wasn't sure whether they meant after the reboot or during. So, I did it when the new Samsung boot logo came on. I guess it's okay.
Oops. It's done. April 2nd security patch.
I'm going to clear cache and factory reset now.
Edit: Everything works. I got my APN settings set up on the device and all of that stuff is working fine so it didn't re-lock my phone. And it's running cool. Not running hot.
Oh, and also that other question I had in the other thread (which I'd forgotten about until seeing it on this update) about my phone displaying LTE instead of 4G reflects everyone's answer there that it is just marketing shenanigans. Now with this new update, it displays 4G instead of LTE. Same carrier. Go figure. I like the 4G better anyway.
So, yeah. All is well that ends well. Only thing I've noticed so far is that when I power off the device, it takes it maybe 10 seconds to power off. With the Lollipop it just powered off right away. Also two tiny little bloatware apps. App Zone app is 1.5 mb and My Account App is 20mb. I disabled both since I'm not with the carrier. Or a resident of Canada for that matter.
Update: The delay that was happening at powering down the device went away so now it's powering down and rebooting without any delay.