@DRender
Take back that Boffin icon forthwith!
Toyota's HSD is a full series / parallel hybrid system and allows the electric drive and engine to operate independantly of each other or in tandem. AFAIK, the only manufacturer kicking out a parallel only hybrid right now is Honda.
So HSD vehicles are exactly like an Ampera with a smaller battery[1] in fact. One of the main reasons the Ampera was delayed was they originally specced the Volt as a pure serial, but found its performance and especially its hill-climbing capabilities stunk like a pile of rotting badgers. The European Ampera launch was delayed while a certain amount of rethinking took place. Allowing it to also drive the front wheels directly from the engine via its epicylic transmission, in effect replicating the series/parallel setup of HSD, involved licensing patents off, er, Toyota.
In certain areas HSD is rather better than the GM tech as it can actually recharge the battery using the engine, something the Volt/Ampera does not do if reports are to be believed (if so, WHY?). This means that the engine can run at its most efficient speed and excess power produced gets squirreled away in the battery until needed. You have to suspect a Vampera's economy in "extended range" (aka flat battery) mode sucks by comparison to the Toyota product and I await "real world" figures with interest.
Given that the fleet market is where most cars go and given the choice of "fill it using the fuel card or plug it in at my expense", I fully expect the majority of Vamperas to run around in permanent extended range mode. This is likely to have two effects. Firstly, the BIK reductions for its headline CO2 figures will make a mockery of the system. Secondly, secondhand ex-fleet cars will invariably come with a shagged battery due to its lack of charge/discharge cycling and residual values will plummet.
All Vampera speculation is IMHO of course, I don't actually have a crystal ball and I haven't had a go with one yet.
I suppose I should come clean (hah!) at this point and own up to having a fleet Prius. No axe-grinding or leaf-munching involved though, it's purely a tax dodge.
[1] Although PHEV versions now exist with a bigger battery.