My experience with a flat with a run flat was under quite different circumstances than most people will experience.
We did Euro Delivery on my wife's 335is Coupe in May 2011 and spent 14 days driving the car through Germany, Austria, Switzerland, and France. Pickup was on Thursday, 5/12. On Saturday, 5/21, we were driving into Trier, Germany and had just exited the Autobahn when the Tire Pressure Monitor warning went off, both in the instrument cluster and on the iDrive. We pulled over and got out to look and sure enough, our run flat tire was about as flat as a run flat tire can be:
We were on a main thoroughfare coming into Trier, so we used the Navigation and looked for the closest BMW service location, Auto Orth, which was just a couple of kilometers away. This was at 16:35 on a Saturday afternoon in Germany, which means that any service-related business is closed. When we picked up the car at BMW Welt we were given a packet of information including a toll-free number to call if we had any problems. We called the number, and long story short, were told that there was nothing that could be done until Monday morning, so BMW put us up in a local hotel for two nights. (This is all part of the comprehensive insurance and trip coverage that is included with European Delivery.) They told us to drive to the hotel and then drive to the BMW service location on Monday morning and call them back. On Monday morning we drove to Auto Orth, less than a kilomoter from the hotel, they put the car on a lift and found a screw embedded in the middle of the tread of the right rear tire:
They don't patch tires in Germany so the tire had to be replaced. The rear tire is a Michelin PS2, 255/35ZR18. Apparently this tire is fairly rare in Germany and we were initially told that it would take 24 hours to get a new tire. Auto Orth did some more searching and found a tire about an hour away, so someone was dispatched to get the tire. Bottom line, the tire was procured, replaced, and we were on our way again around 14:30. The worst part was that we had to pay for the tire, since tires are the only part of the car not covered by the no-deductible all comprehensive insurance by Allianz, provided as part of BMW's Euro Delivery option. The charge that came through on our credit card statement was $580 for the tire, mounting, and balancing.
Our plan had been to spend a few hours in Trier then drive to Cologne where we had a hotel reservation for Saturday night. On Sunday morning we were going to get up and drive to the Nurburgring Norschleife for a full day of Touristenfahrten. We had planned to buy a four-lap ticket, two for me and two for my wife. After that we were going to drive to Rothenburg ob der Tauber, where we were going to spend Sunday night, all day Monday, Monday night, and then head back to Munich on Tuesday where we had a reservation for Tuesday night, and our return flight on Wednesday morning.
So how did having run flat tires affect us in this circumstance? Because it happened in Germany on a Saturday afternoon, even if we had a mini-spare, there was really nothing different that could have been done and a new tire still couldn't have been found until Monday morning. Cologne would have been too far to drive on a mini-spare, particularly on the Autobahn. Since the whole purpose of driving north was to drive at Nurburgring, we wouldn't have done that on a mini-spare anyway. A full-size spare would have been the only way that our trip could have continued uninterrupted. But our car has a staggered setup with 225/40ZR18 tires in the front. So what size should the spare be? If it were the 255/35ZR18 rear size then having a flat front tire would result in having a mismatched front set. If the spare were the 225/40ZR18 front size, then having a flat rear tire would result in a mismatched rear set. Bottom line, there were no other alternatives that would have resulted in a better outcome.
If this had happened to us on a Saturday morning on our way to Costco, then the outcome would have been much different. We would have called BMW Assist (BTW, BMW Assist isn't enabled in Europe, different radio frequencies), the car would have been flat-bedded to a local BMW dealer. If the service department was still open and if they had the tire in stock, it would have been replaced and we would be on our way. If not, then we would have been give a loaner, we would have gone on our way, then returned to the dealer on Monday afternoon to pick up our car with a new tire. If we had a mini-spare then I would have had to change the tire, possibly on the side of a freeway, and a visit to the tire store would have followed. Alternately, call AAA and either have them replace the tire or flat-bed the car to a tire store. Bottom line, a flat tire is a bummer, and interrupts your plans, and regardless of whether you have a run-flat tire or a mini-spare, it will result in a trip to either the BMW dealer or a tire store.
Now, about the run-flat tire itself and the screw that caused it to go flat. From the time that we exited the Autobahn until we got the warning was less than a kilometer. We drove less than two kilometers to Auto Orth, only to find it closed, then less than a kilometer to the hotel and less than a kilometer back to Auto Orth on Monday morning. Take a good look at the screw in the tire (the pictures don't do it justice, the head of the screw had been ground completely flat). Do you think that the screw would have been that damaged with only a few kilometers on it, in other words, did we pick up that screw after exiting the Autobahn or did we pick up the screw on the Autobahn or before we got on the Autobahn? Prior to the exit we had been driving for several hours at speeds of 110-120 MPH (not KPH!) and had a brief run at 145 MPH. When my wife saw the screw in the tire she said she sure hoped that we had picked up that screw after we got off the Autobahn. My reaction was the opposite, I said that I hoped that we had picked it up and driven on the Autobahn like that, because that would be a huge testament to the safety of run flat tires.
Different circumstances result in different outcomes, but this was our circumstance and our outcome. I don't think the outcome would have been any different, regardless of the type of tire and flat tire remedy.