While I appreciate the advantages of the run-flat for BWW, the tires available presently are horrible. I've only experienced the Bridgestones, but they're not a good tire. I got about 15,00 miles on the tires that came on the CPO 325i I bought and even less on the replacements... about 12,000 miles and the shoulders are at the wear indicators. This in spite of running them at THIRTY SEVEN PSI (37 pounds pressure). Bridgestone "kicked in" for the original's replacements at 12,00 miles for 1/2 price and told me to run them at this ridiculously high pressure. This is the pressure one see's in truck tires. I can feel every little bump and imperfection in the road.
I'm going to go the non-run flat option, although I'd like to hear from those who plan on carrying a spare first... You gonna carry a front or rear? They're different sizes you know ( or do you?)
I'll carry an on-board compressor and keep an eye on the tires. Most times if one has a problem you'll notice it if you actually look at it. Be wary about any repair material you put into a tire. It will probably ruin the Tire Pressure Monitor (TPM). These things cost about $60-$70, although a dealer will likely charge a couple of hundred to remedy.