I have a duoX2 - basically, the thing to consider is what will you REALLY be doing with it? do you need all the functions of the expensive ones? Mine was $15, and it supports all xboxes, has 2 bioses so i can boot to whichever i want, and functions extremely well as a modchip.
In the end, all it does is boot the box to a different file - is it really worth it to you to spend $80 for the same functionality? IF all you're going to be doing is running a modded box, go cheap, it makes more sense. If you're a programmer or whatnot, maybe look at somethign more expensive.