The MiFi looks like a real product supported by carriers. The GMate looks like a funny little thing I hardly get any Google hits. That doesn't mean it's bad, but...
Since you're asking the question about what appear to be two very different things, you're obviously not an expert (I'm not either, at all). The GMate seems like it is for tweakos, ergo, you should go with the MiFi.
But there are a number of hotspot products. I think you should search for threads comparing hotspots, and start a thread "which is the best mobile hotspot?" if you don't find good answers. And a hotspot isn't just the hardware & speed-be sure to ask about plan costs, signup fees, contracts.