TL;DW
The PoE shield for the Raspberry Pi3 provides power without the need for a micro USB power supply. However the shield itself has some questionable safety gaps between 48V from PoE and 5V supply side.
Example 1:
Example 2:
The next problem is the supply current at the USB ports. The thing drops out at 50mA (0.05A). USB-keyboards with background lighting will not work.
While this (probably) won´t damage anything and a Pi will idle along just fine, it is something to be aware of when using USB devices.
Case of piss poor design:
