One I got about 3 years ago is about 50% as efficient as a glass panel I got about 0 years ago. Not exactly a scientific study, I know.
I don't have a number, but in general, no one uses a flexible panel unless they are compelled to. The efficiency is lower, and my experience is that they don't last. I had one a few years ago, and it lasted less than 2 years. My rigid panels came with a 25-year performance warranty, and are still working great after 7 years.
Up to now, it has very poor efficiency, about 5% to 23%.
