Happy to be corrected by any CVT driver out there.
PS I don't think the Jazz has "brake hold".
You're correct about the CVT and Idle Stop issue. It annoyed me at first but so many people do keep the foot brake pressed when stationary (regardless of transmission) these days that I've learnt to accept it. It never really dazzled me so I'm happy to take the view that if you really are being dazzled you should go to an optician
What irritates me most about the CVT I/S implementation is that the engine restarts even if you've selected neutral before releasing the brake pedal. The silly thing is that it will restart if you move the selector out of N so in that case there is a perfectly good indication that you want to move.
As for how much fuel it saves the last time I looked on the web most technical sites were saying that as long as the engine is off for at least two seconds it will save something. Estimates vary but in several 'real world' tests I found it seemed to about five to ten percent for urban driving. That equates to reducing the price of a litre of petrol by 5p or more and I bet most of us would consider that worthwhile
However you're wrong about 'brake hold'. My EX has it.
Edit: Re, idle fuel consumption https://energy.gov/eere/vehicles/fact-861-february-23-2015-idle-fuel-consumption-selected-gasoline-and-diesel-vehicles
For a 2 litre petrol engine it's claiming .16 gallons an hour or .6 litres an hour. So that's just over 1p a minute. So very approximately I/S could be saving me £2 a year. Hardly worth worrying about. But if we multiply that by the couple of hundred thousand vehicles on the road that have this feature (assuming most leave it on) and the fuel savings become more significant.