Both are battery-powered devices and the Overdrive does everything the MiFi does but, with the addition of 4G, it has the potential to do it much faster. How much faster? Well, a 4G device should be able to provide anywhere from 100 Mb/s to 1000 Mb/s, depending on usage and locale. As well, 4G is absolutely, positively, maybe guaranteed to offer seamless hand-offs as you leave one coverage area and enter another. The only problem is that there aren’t that many 4G areas just yet — but they’re coming, and the Overdrive offers 3G compatibility should 4G service not be available.
Personally I am so close to canceling my MiFi contract and getting the Overdrive. It looks and sounds sweet.