From my experience (driving 30k in 1.5 years) I see a severe reduced range in the Leaf during the winter. In a cold snap in Texas WITHOUT USING THE HEATER, I get 10+ miles less range (sometimes 15 or more) than I do in the summer running AC. That has nothing to do with the heater consuming power becuase i just suck it up. Did we all forget Tony's range chart? For every 2 degrees below the sweet spot (in the 70's I forget the exact #) it looses range. This was done by Tony after extensive testing. The TMS WILL allow the battery to opperate at a better temperature and therefore give you more range. My wife's Volt - in the summer (mostly 70/30 highway/city split) she gets 50+ miles of range (yes 50, her work is 50 miles away and she can make it on battery alone). Winter time? 45ish. That isn't a large difference. Me on my Leaf? Summer time (at 2 bar reduced capacity) ~72 miles (mixed 65/35 at my best). Winter time (like freezing or below) I get ~58 miles of range. That is a greater wild swing that the Volt every will get.
As for the Volt (i.e. a lower vehicle like the FFE) on the highway, hell yes it does way better. Highway in the summer (all highway) my wife can pull 45-48 miles. Me on the Leaf? 60. Now take that I have 2 bars of loss already, but considering I should have ~75% more battery available (17-18 kWh vs 10.4) I should get a greater increase in range, not the punny amount i get now. In Texas EVERYTHING is highway driving, so the comparison is more pronounced.
For TMS usage, if the FFE uses it even when not plugged (like the Volt), I have found the drain to be extremely minimal. On the Volt boards most calculate that the TMS uses ~400-800 Watts per use and usually will only run once every 2-4 hours. My wife nor I have seen very little impact to range while letting the Volt sit not plugged in. fortunately I don't know the FFE's TMS and it's usag, but they Volt's usage has never depleted an entire bar before, so it's not that power intensive.