"Seems pretty dodgy."
Sure, and I've seen the rants against the extension cords with boxes mounted on the ends of them, with (at the minimum) the assertion that pendant rules apply.
Another maven of the seminar crowd recently crowed that 'changes' to OSHA rules pertty much ban the use of anything home-built where there is a listed product manufacturered. (Alas, he used the entire CFR as his citation, so I have yet to find the 'change' he was referencing.)
Balderdash! Since when did we make individual effort illegal? Maybe stick-built homes will be banned next, as there are many fine 'manufactured and UL-listed" homes available!
Just because something is site-made does not mean it's automatically wrong.
I applaud the guy's effort at making his own 'spider box.' Please note that most 'factory' boxes have far fewer receptacles, and use twist-lock types instead. This guy has the bases covered: support, over-current protection, strain relief, etc.
While I might have done it differently, those are differences in design only.
Let's face it: despite the tremendous range of products available commercially, there are still situations where the factory-,ade products are lacking. Perhaps the most obvious is the lack of space; plug in one 'wall wart,' and you've taken several receptacles out of service. That just might be why there are so many receptacles on this board.
If - and it's a big if - one were to find fault with this product, it would be the lack of GFCI protection. That is an issue that can be readily addressed just by replacing a few receptacles.
