I ride with one on my Brompton. It does not reach quite reach the versatility of a chain but gets close and is lighter, i.e. a good compromise particularly in the case of my folder. Seattle is actually one place in the US where you can encounter them at some frequency. There was a photo on BromptonTalk of one that got cut in Paris a year ago or so. (Yes, it was the 6500.) Still it seems to be a relatively rare case and you need to plunge one way or another taking the risk.