My gut feeling is no... You get 2 joys, 22 buttons, "pc electronics" and some interface / mode switch stuff. That's not apparently any of the box itself. If you're simply building a controler for your pc like the x-arcade unit, could be ok. If you're building a whole machine, why not just get exactly the parts you need?
$99 seems pricey for the parts. The joys and buttons are probably a total of $30, an IPac is $39...
If their layout suits you perfectly, and you don't like working with the construction, you could pay 140 and get their panel complete, THEN build a cabinet to go with it.