I ordered the 27-29 inch gray boxer briefs (I wear pants with a 28 to 30 inch waist and so did the person in the review I read. They said the 27-29 inch was perfect on them). It is for me too. It rides low on your hips so when you put in your packer it will probably fall in an anatomically correct position. This reviewer didn't have such luck, which is weird; we both have the Goodfella and it sits just where it ought to on me.
It's a bit difficult to finagle this particular packer into the O-ring but it is possible. You can either back up the end piece into the ring itself or slip the shaft through the pouch in the opening, leaving the balls and end piece inside the underwear. Either way works just fine. But for the Goodfella you might have to practice the former before you're in a situation that calls for fast action... or at least excuse yourself to the bathroom so the other person doesn't have to watch you fumble with yourself.

I really like it so far. I don't know if I'd recommend soft packing with this harness, but I think I've heard of people having success with that, so take that particular advice with a grain of salt.
Unfortunately it might be a while before I'm able to use this with a partner. I'll certainly report back my findings then, but for solo stuff this combination hits the spot. And for the price, it's worth giving it a try. I'm glad I made the decision.