Because it's made by MAC Valves, WAS just sell them under their own name.
It's a direct acting noid so draws quite a bit more current than most others (Think it's 4W from memory), you may find your board just shuts down if you try to use one.
Most decent boards can supply enough power to operate the mac noid, but you need code written specifically to power a direct acting solenoid, otherwise you will eat your battery as Flash has pointed out.