EV Mode limit is 10mph.... is this right?

Go with that. Use it for the occasional garage to driveway shuffle, IF it'll work.

 

First of all, it's important to note that there are two different kinds of "EV Mode". The mode you're talking about is the one where you press the "EV Mode" switch to request that the car run solely on electricity. That mode is limited to something like around 8 to 10 MPH (it cuts out at around 15 km/h on my Canadian Prius C).

The other mode is initiated by the car itself whenever it senses conditions that make it more efficient to run on electricity (which of course was previously generated by the engine anyway). The car uses the current battery level, state of engine warm-up, load on the engine, speed, and probably other factors to decide. The car can initiate EV mode on it's own at speeds up to 74 km/h (around 40MPH).

So - is it worth it to push the "EV Mode" button to ask the car to run on electricity only? The answer for me is yes - I routinely put the car into EV mode when I'm backing out of the garage so that the engine won't come on until the door is closed and I'm ready to proceed. Since the engine always fires up when the car is started from cold I like to be moving so as to get some benefit from it rather then just be fiddling around wasting the fuel.

In fact I often travel the couple of hundred feet through my back lane to the street in EV mode so that I can wait for a traffic opening and get moving at full speed before the engine comes on. The Prius C is smart enough to use electric propulsion only (unless you really mash the throttle to the floorboard) for the first dozen or so seconds of engine operation to ensure that oil has circulated before putting it under load, so I'm happy to do this knowing that it won't have an adverse an impact on it.

 

Does the 'c' have the same engine temperature dependence as the Liftback?

For my Liftback, the EV button works up to 25 MPH when the engine is reasonably well warmed. Below 68F, it doesn't work at all. In between, it works to 10 MPH.

These temperature limits are specific to North American models. European market models can use EV down to freezing level.

 

Ditto. Never had to use it. I actually don't have that button. That's how useless it is.

 

Yeah, the EV Mode button isn't effective when the engine is cold. It also won't work when the battery isn't reasonably full - I've never paid enough attention to know for sure but I think it might need around 3 or 4 bars of charge.

I installed a block heater and I often use it in the winter to pre-warm the engine to minimize warmup times. It's enough to let me engage EV mode even if the car has been sitting in cool temperatures that would normally preclude it.

 

Yes - it won't come on if the car's been sitting in pretty cool or cold temperatures. And it needs a certain minimum battery level as well, perhaps 3 or 4 bars.

I installed a block heater in my Prius C to minimize engine warmup times and it lets me use EV mode at colder temperatures than would otherwise be possible.

 

Not exactly right. It is the EV BUTTON that is useless......since the computer will over-ride it for lots of reasons.
And yes, if you do push it, it likely will go off around 10 MPH.
The computer does NOT like being told what to do !!!