As the title says, DO NOT download the Android 4.4 KitKat update if you want to keep your Note 3 usable! This update is riddled with serve phone disabling bugs and removes the ability for apps to write to the SD card in your phone! If WiFi calling is necessary then stay away! The update will kill your battery by half or more (I used to get two days or a little less and now I'm lucky if I make 8 hours). The update was nominally under the hood updates and nothing really changed other than for the bad. There is now a 5 bar signal indicator (which will make your phone look like it has a better signal as the one bar you used to get in your home will now be two bars. The keyboard is darker and has a few new emoji and emoji are the same throughout all apps (hangouts now uses the traditional Samsung emoji rather than a complete different Google set), icons in the notification bar are now white and the font is Roboto Light vs the old Samsung font. Also persistent notifications no longer have their own section in the notification bar (they are now bunched with everything, EG: Music apps, remote controls, etc), which is annoying at best. That is about it... So the chances are you'll have a million headaches over white icons and a few emoji. DON'T UPDATE!
Long list of detailed issues: Huge battery drain (with Android system and Android OS taking the top two spots next to screen time), GPS issues (takes forever to lock, sometimes will show me at old locations, never shows exact location, always a few hundred feet from spot EG: while driving it looks like I'm on the road parallel to me), WiFi Calling issues (works for the first half hour and then calls and texts stop coming in but the phone looks like normal but you miss call and texts and once you leave WiFi or turn it off you get hit with all your missed texts), WiFi calling also when leaving WiFi area the phone is unable to switch the normal cell radio back on and I get a no smoking sign where the signal should be and I am unable to make calls or text, only a phone reset fixes it), some restarts and freezing (sometimes the phone comes back after a while sometimes a battery pull), I know this is a "feature" as Google calls it but the SD card needs to be modified so it can be written to (KitKat be darned Samsung needs to find a way as it can be done if you root), data speeds are slower and a few more I can't think of.
After doing T-Mobiles recommendations of a SIM pull, battery pull, reset, and finally a hard reset (master reset which deletes everything on your device) my issues are right back. They wanted to send me a replacement (used mind you) and I refused. My phone is in mint condition and worked fine the day before the update and I didn't spent $800 (bought outright) for a used phone! If they offer me a new one with Android 4.3 I will take it and I'm writing an article for consumerist and a few other outlets now. I really can't wait till they push this update to all the Note 3 owners as that will be the only way to get them to fix it ASAP! I have two Note 3's on my account and my parents have two on their account in another state and all 4 have these issues! The OTA push should be happening today or in the next few days! Then more people will have the issue and we will see some movement on the issues. And T-Mobile still won't admit there is an issue but they will have to once every Note 3 owner gets the update. Many haven't experienced the bug because they don't use WiFi calling and I believe this is the catalyst for many of the signal issues.