I've been using the Belkin one Apple sells since November with zero problems. I have it attached to the LG5K display so my system switches to ethernet when I attach it to the monitor.
Have the Belkin one and I don't see any speed differences vs my wifi. It could be my speeds. I have ATT Gigabit service so On laptops usually about 400-500 up/down. It gets warm.
I have the one from KANEX and it works great with my Early 2016. I get the full speed my cable (TV) Internet provides 400 Mbit/s download (never got that over WiFi). Even if I attach it to my USB-C dock from Caldigit with several other devices connected it doesn't slow down.
The best thing was, it seemed to be a gift from KANEX because I ordered a few cables on Amazon from them and I didn't pay anything for that Ethernet adapter.
A little off topic:
That dock also has an Ethernet port but they don't seem to update the driver for it (still version 1.0 and states to support El Capitan max. and I am on High Sierra).
Maybe it's just an APFS issue that will be fixed after official release, didn't try it with Sierra yet. It is visible in the Network settings but says not connected.
The driver is only needed for the Ethernet port, all other ports just work. Even for an external optical drive, they claim it's needed for SuperDrive support too, mine is another brand. Could also be just for BootCamp support.