These a great quality heated bed with a few extra features that you don't find on the more standard beds out there.
The first is that these are dual power and can be used with either 12v or 24v supplies, just choose the appropriate connection pads on the board.
A small hole in the very centre allows a thermistor to come through and be in direct thermal contact with the print surface so you can get the most accurate readings possible.
Finally there are 5 mounting holes, 1 at each corner, and another in the middle of one edge - this allows you to have either the more normal 4 point mounting, or alternatively a more easily levelled 3 point levelling system.
This bed is dual power and can be used with either 12v or 24v supplies, just choose the appropriate connection pads on the board.