Macworld has an in-depth review of Sierra Wireless’s Overdrive mobile 4G hotspot. It’s the Mi-Fi for 4G. Apparently, it’s not a performance win for devices such as the iPhone or iPad that have their own 3G radio built-in. Seems to work great though for laptops. The review is actually a pretty good match for my use-case.
But if a smartphone can serve the same purpose, with the same performance, that’s one less device to carry. The only upside is that the mobile hotspot might have better battery life.