Zigbee is very low power and much higher frequency. You have to be within a couple dozen meters.

The goTenna thing is much higher power and lower frequency. It reaches at much greater distance, and can even go a bit around small obstacles (it's 2m band, so don't expect miracles, but still, it's not 100% line of sight).

Zigbee: "Outdoors with line-of-sight, range may be up to 1500 m depending on power output and environmental characteristics"

I'd buy one of these GoTennas before you get too excited about the range.

"Oh, but it's VHF so you can get Es propagation and talk to Europe from the US!"

Good luck with that.