Just thought I'd follow up my original post. I've used these continuously for maybe 6-7000km with no problems. They are starting to look very worn, especially the left one from putting my foot down, but they haven't broken yet and I expect them to last for some time to come.

I would definitely recommend these if you have to negotiate stairs on a regular basis, or you just need to walk a bit on your Speedplay cleats. Not having to carry the covers around in my pockets is definitely a good thing.