[Android Software/Hacking General [Developers Only]] Oswald Boelcke:
This post does not contain a bug report but only some personal observations!

For my device configuration, please refer to the hidden part of my signature block if interested. Prior to the (short time) conversion to PHH's SuperUser I was on SuperSU v2.78 by CCMT (formerly developed by Chainfire). The reason why I wanted to get rid of that are explained in this post.

Flashing of PHH's SuperUser.zip worked without any problems in both ways i.e. applying either "full unroot" or "switch superuser" in the still installed SuperSU v2.78 prior to booting into recovery. Even after "full unroot", the SuperUser.zip clearly re-roots the device. I also realised that at least I had to install the SuperUser-Interface-APK after flashing of the SuperUser.zip. When I installed the APK while SuperSU was still installed, when opening SuperSU to either apply "full unroot" or "switch superuser" I received a warning about two superuser installed (however, the second was only the GUI) and a question if I wanted to delete the second one. I denied the latter. Despite that, after flashing SuperUser.zip and restart, the SuperUser-Interface-APK wasn't available on the system.

PHH's SuperUser provided me full root management; however, one annoyance and one problem that definitely dragged me away from PHH's SuperUser and back into SuperSU but reverting to v2.76 (definitely by Chainfire).

Only annoying was the permanent notification when opening Titanium Backup about a superuser binary that might create problems. Even if I ticked "Don't show again" the message came up every time I opened TB.

My severe problem was that I was positively connect to data after restart but never achieved an internet connection - neither on WiFi nor via mobile data. I'm convinced this wasn't an issue of SuperUser but of my IPTables. All my root apps requested root access and got it granted by SuperUser except one: AFWall+! For whatever reason, AFWall+ did not request root while I was on SuperUser i.e. I was unable to modify the IPTables and was stuck with no internet connection. After conversion to SuperSU v2.76, all was back to normal i.e. root access for AFWall+, too.

Summary:

Easy and successful flashing of the SuperUser.zip.

Good and easily managable GUI.

Positive root management by SuperUser.

The severe problem with only one application (AFWall+) made me not to use SuperUser as my daily root management tool.

Edit (2016-09-18): Next time, I'm going to flash my current ROM (e.g. for a revised version) I'm giving PHH's SuperUser another try.

Edit (2016-09-19): PHH's SuperUser incl. the former troublemaker AFWall+ (Beta) now succesfully working!

Dirty flashed in this sequence: ROM, GApps pico, AGNi, Xposed, SuperUser.zip; SuperUser-APK was already installed, as I had flash superuser.zip and installed the APK even prior to flashing the ROM but at that point AFWall+ didn't asked for root. Therefore uninstalled AFWall+, fully un-rooted the device by SuperSU v2.76, and then commenced the above flashing sequence.

Two remaining issues:

AGNi Control requested and got root granted by SuperUser; however, when opening AGNi Control none of the tweaks is visible. I'm going to post that issue in AGNi thread.

Edit (2016-09-25): Root Essentials is still stating in its module "Root Checker" that SuperSU is the root manager. All other applications state SuperUser by PHH to be the root manager. Going to post Learnt at [APP][3.0+] Root Essentials that the application actually doesn't indicates the root management tool used but the mentioned tile is only a link to Google Play Store to allow download of SuperSU i.e. from my point of view it's an advertisement for SuperSU v2.78 by CCMT.