BMW run-flat tires -
0/  There is no spare in the trunk, no jack, no tire maintenance facilities whatsoever
1/ The runflat tires (RFT) can usually not be repaired in the case of a puncture,  (manufacturer discourages ad-hoc tire patching - warranty implications)  so instead of a simple puncture costing $20, you've got to replace "a PAIR "  of tires.
2/  RFTs can malfunction, defeating their intended purpose to begin with, or be damaged in such a way that getting the typical 150mi@50mph is no longer possible.
3/ RFTs are more expensive to buy/install & offer poorer performance.
4/ Lifespan is half that of normal tires on average.
5/ The ride is more uncomfortable, especially if you have 17" upwards.
6/ Increase the running costs of ownership.   Normally a tire lasts a good average of 80,000KM.
6/ On a road trip u could get stuck in a dangerous unfamiliar stretch of road - especially afterhours. BMW stealerships are not everywhere.  RFTs are not common & not all shops stock them.