Are run-flat tyres worth it?

I have ordered a new BMW X5 which only comes with run-flat tyres on 20-inch rims and an emergency inflatable spare. I like the car but I think the ride quality is compromised. The dealer is happy to change the rim size to 19-inch but the run-flats remain. I have no issues with putting the spare on if I get a flat, so do you see any downside with replacing the run flat tyres with regular tyres?

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