[Xperia Z3 General] arikdahn:
Can confirm the KingRoot method works well. It's quick, painless, and easy. It does install some bloat and enjoys doing so moving forward if you go tinkering in the app settings. Everything you click on installs a new bloat app you will have to remove. Furthermore you MUST turn off the lock screen bloat app that comes with it because it will not power up while plugged in with this enabled. I made the mistake of sitting on the couch and running it dead after I installed KingRoot. Then I plugged it in and it would not boot. After panicking and then some screwing around I discovered once I unplugged it, it booted fine. Then I plugged it in and it crashed when the King Root lock screen came on. This option comes pre-enabled with the app. Once you disable it, no problems. I am still researching the safest/easiest way to install recovery for protection reasons and then switch to SU as the root manager and I think you have to have recovery to install xposed so you can get youtube ad-block

I also do not like this Kingroot craptastic app for long term root usage since it nearly caused me to think I broke my phone. Doing so may be as easy as installing SuperSU from the market and then uninstalling kingroot, but I somehow doubt it. Kingroot is pretty possessive of your device. Uninstalling it removes root vulnerability exploit. Because I don't trust it, I am scared it might intentionally brick my phone if I tried to **** with it.

Because the bootloader is perma-locked on these phones, you cannot install any other ROMs aside from the included SONY one but as christoph34 claims, it works great and there are a variety of launchers you can use to make it more friendly to what you want to do with it. The ONLY gripe I have is that you cannot change the system font on this phone. It baffles me why Sony did this. Otherwise this phone is completely contemporary looking and operating, and it has no lack of important features except for fingerprint scanner which I do not care about.

Also [MENTION=7803635]christoph34[/MENTION] I would like to thank you again for your help.

EDIT: I lied. I had another xperia z3 originally and it crapped the bed (would not charge) within a few days of me purchasing it, so I ordered another one and the bootloader is totally unlockable. I am going off what the previous phone showed and what other owners were saying about it, so it appears you actually can unlock the bootloader on some TMO Z3's.

You cannot use SuperSU just by installing Kingroot, then installing SuperSU, giving it root permission, then uninstalling Kingroot. With SuperSU left installed, Kingroot will not uninstall. It may not uninstall at all honestly - not completely sure. I only tried to do so with SuperSU still installed. It does prompt to uninstall both Kingroot and SuperSU when you attempt to uninstall Kingroot, but I have only tried uninstall Kingroot and leave SuperSU. Almost anything beyond root access would be useless using Kingroot as a root manager. All other procedures I'm seeing for this phone to do thing like install recoveries and xposed modules indicate clearly they only support SuperSU as a root manager. It does not seem like Kingroot is feasible as a root method if one wishes to install a recovery as well.

Given how how eager-to-brick Sony and TMo made this thing, I am scared to experiment too much. I will say the primary motivation behind wanting to do this is blocking ads. It makes tons of sense that they would make it borderline impossible to avoid having ads forced on you given how lucrative it is. I might just leave it rooted with kingroot and hope it's not sending all my PII to china. I am too scared I'll break this thing. Plus the dev team here never spent much time on the D6616 and any attention it once garnered is now completely gone. If there are ways to do basic android things, nobody can remember if they still work or not.