How?
There are a few significant differences: biggest one for me is operating system. The IVP is probably going to stay on 4.2 forever, whilst the Zest has 4.4 and OTA updates.
The OS is very significant in a phone at this price level, especially with KitKat having lower requirements than Jellybean.
Other differences:
Better camera
Less bloatware
Higher resolution screen.
Slightly faster processor
The other, slightly more subtle thing for me was the lack of a decent review of the device. The only reviews I could find were ones by kalahari and a brief video one by EWN. No camera photos, no benchmarks, no videos of games being run.
Compare that to MyBB's thorough review of the Zest...
The choice is pretty obvious