I used to have them w/ some Borbet wheels. They tended to stick to the wheel sometimes, so I made sure to mention that to the Discount tire guys eveytime I went in for a balance/rotation. They mangled them more than twice, but always got me news ones... at their cost... via Tire rack. At least w/ mine you could run without them for a short while.
The Mille Miglia wheels I have now have a hard, black polymer type that are a lot more thicker and sturdier than the metal ones... I have had no issues at all w/ them.