I'll be very interested in your experiences with energy use with the two types of tires. I don't know anything about the runflats that BMW chose for the ActiveE, but my guess is that they are among the most efficient of the runflats available, at least that is what I'd chose if I were at BMW.
I had a 2008 328i coupe/sport for three years before the LEAF and I was very interested in the runflat issue then. At the time I was shopping for the 328i, the common experiences with the Bridgestone runflats were noise, weight, poor tread wear life, sidewalls easily damaged, tramlining, and the expense and poor availability of replacement tires. If you got a flat, you could usually drive slowly and safely home or to a tire place or BMW Center, but then your car might be out of action for a few days while waiting for a tire. Some drivers got very poor tread wear, to the point of needing new tires in less than 10,000 miles, sometimes much less. BMW replaced some of the Bridgestones with Continentals, which were better in most regards, and at one point BMW had an unwritten policy where they'd replace the tires at part or no cost if they were under a certain mileage and they had certain kind of wear, usually edge wear.
I only drove my BMW 18,000 miles in the three years that I leased it, and I was concerned about being able to return it from lease without having to pay $500 to $600 each for replacement tires. I got lucky and the tires lasted my entire lease without wearing out. That was mostly because I didn't drive very aggressively. Aggressive drivers got much less mileage from their Bridgestones.
I haven't kept up with the developments on the BMW forums since I returned the 328i, so I don't know how things have progressed on this issue. My guess is that there are more choices in brands and types of runflats, more availability and lower prices, all of which are good things.
