It's very realistic in terms of my typical usage: I do about 300 kms/week, and the BMW i3 I've been looking at has a real world range of 200 kms (plenty of people stating online that they get this). I live in Dublin, where there are planty of charging points.
I've test driven one, and it's an amazing car to drive. I'm used to silent running from my Prius, but this remains very quiet regardless of speed. It rockets off the line if you want it to (though no doubt this would affect the range if you did it every time). Although relatively small inside, it feels roomy and is a very pleasant place to be. It is quite expensive, though, even with the various VRT rebates etc. that electric cars get. However, the BIK reduction (since confirmed to be 3 rather than 1 year) makes a huge difference to affordability. I've yet to run the numbers, but I suspect it'll be quite a bit cheaper for a company car than anything even remotely close to it.
Regardless of how it's done (i.e. purchase or lease), for someone with no business mileage with a marginal tax rate of about 50%, as far as I know, the cost to a company to give the use of a car is roughly double the cost of the car, if take-home pay is kept the same. Is this correct? If it is, a 0% BIK rate is a very serious concession.