"Placing the BFG PSU in the case, we can see how much space both of these take up. It's really not all that much, as all of this is behind the primary motherboard. There's still a more than 30cm of free space over the PSU."
Looks like there are two PSU's in there. It seems like a bit of overkill, but a 75W Pico PSU (I got one) requires somewhere in the range of 3.5+ amps @ 12v for stable operation, so I don't know how well a average (500W) PSU would enjoy having to run the Pico on top of a regular system.