It's a change like any other but I prefer the idea of runflats to regular tires with a "fix-a-flat" kit; which is what they're doing with the CLA45. Just keep in mind that you can generally drive up to 100 miles on runflats without any air. Also, you can plug them just you like would plug a regular tire. I've posted pictures of a blowout my cousin had with runflats on her rental car in other threads. She was able to safely stop her car from 75mph without any tread left on the rims without damaging herself, anyone else, the rim or the car. The rim showed no signs of curb rash even. If her car had been riding on regular tires she would have destroyed the rim at a minimum.
The only arguable downsides to runflats are cost and some people complain that the ride is harder than with a regular tire. A fix-a-flat kit gets you none of the benefits of runflats and all of the downsides of a regular tire without a spare. PLUS, you get the added benefit of ruining your tire (so that you can't plug it) and your rim (the goo you spray into your tire also coats/destroys the rim).
-Eric