In my opinion, all these "range extenders" are just ways to take advantage of people's range-anxiety. EV's are wonderful, clean, quiet, low-maintenance machines, and lugging around a gas generator completely negates all of those things. If your commute is the sort where you have to fill up with gas every day, then an EV is not for you.
Driving my Leaf is like driving on a quarter-tank of gas. Anywhere a sedan can get you on 1/4 of a tank, the Nissan Leaf or Chevy Spark EV can get you there, too. That doesn't sound like much, but since you will be fueling up every night it's really not that bad.
Driving a Tesla (or the up-coming Chevy Bolt) is like having half a tank of gas (maybe a little bit more).
If range is a concern, then the plug-in hybrids like the Volt are a fine option. They still carry with them the added expense of maintaining a gas motor, but at least it is fully integrated into the design of the vehicle.
Driving an EV is like living on a budget: it involves a bit more planning, but you get more value out of it in the long run.