I mean, for the all-electric distances it's pretty much a given that it's cheaper: fuel consumed is the largest item on airlines' expenditure. The bigger question is at what distance you start having to burn more fuel than if you weren't lugging batteries round with you. If it's [eventually] commercially competitive at 400m range it's going to be useful on a variety of routes currently operated by ATR-42s and Saab 340s etc, the sort of thing that's definitely not operated by 40 year old 9-seaters. If it isn't... well islands still exist, they're just a fairly small niche