You get what you pay for!
Yes, they're expensive. Yes, the little "Speed Shields" ad a modicum of weight (and potentially imbalance your cost-no-object wheels.) But they are ROCK solid, allow NO air leak, and insure silence on any tube / tire / wheel connection. I first experienced these when they were packaged with my Silca latex tubes. When a set of my tubulars needed new extenders due to getting gunked up with a little too much sealant (yes, I run an ounce of sealant in my tubies) I went for these. As usual, Silca delivered, just like they do with their wax products and tubes. #HappyCyclist