the 2nd PCB and ribbon cable are a really good addition (in theory)....
(its something I've also done something very similar on some previous builds)
however...
the execution on this kit is really poor/shoddy (IMHO)....
this kit has been knocked up (ripped off) by someone that hasn't built any by the looks of it...
(or they would have come up with something a bit more practical)
the idea of the is to make the build a little "easier" and cleaner by just having a ribbon cable connected between the button PCB and the RPi
obviously, you'll have to solder ribbon connects on both PCBs and solder the second PCB directly to the RPi
where this kit fall short....
is which GPIO they've used for the buttons (which limits you a little when putting a build together)....
but more importantly they havent bothered supplying the people that buy these kits with the GPIO layout, which means most novice builders have been put off by using it and just solder wires from button PCB to RPi
(which kinda makes this addition a bit pointless and a bit of a waste)
and then you also have the length of the ribbon cable (but you can get a shorter one)
NB: anyone wanting to use the 2nd PCB and ribbon cable and isnt sure about where everything goes (GPIO).....
just use a multi meter and test the continuity from the button PCB to the 2 PCB/RPi (it isnt rocket science)
.