Nice looking cab guy. One thing I will add is that there are a few home emulated games that use 6 buttons on player 3-4 (hmm, at least I think there were...) so at least you can play those games with Hyperspin.
As for the OP, I have both home built systems and purchased ones (Slikstik) and they both have their advantages and disadvantages. I say go the purchase route if you don't want to do the work. THERE IS NOTHING WRONG WITH THIS, contrary to what many on these forums make you feel.
BYOACers, remember, part of the BYO also applies to software, so there is nothing wrong with coming here and asking for help/price comparisons on the hardware side before going on to the software side.
Remember, we're a friendly community, here to help, right?
EDIT: Wow, that took awhile to appear, glitch! Anway, yes it has been stated about the home systems and extra buttons, but anyway, good luck with your decision!