I tried using the pump and slime provided in my M5 once - it didn't work. I don't think the slime ever came out of the canister.

I have since moved to carrying a jack and tire plug/patch kit in my cars without spare tires (which is almost all of them at this point). I have great success with the patch kit on the M5. Fixed two flats with it and then drove it to the tire dealer for a proper repair (or replacement). BMW has a great (although overpriced) jack kit for their sedans that fits in the side trunk compartment on my M5 so I don't lose any trunk space. In the X5 I have the jack and patch kit in the storage area under the cargo floor.

The only situation I would be SOL with this setup is a complete tire blowout and I haven't experienced one of those in many years.