Good question. It looks like they are about the same length but about an inch wider. I guess you could look at that two ways....they're wider and may work even better or they're wider and might be more vulnerable to getting hit by something and causing damage and since they're wider they're catching more air and exerting more force on the unsupported fairing possibly doing damage. Personally, I wouldn't worry about the small bit of added force since I don't notice any flexing of the fairing with the BMW winglets.
I had no idea when I first started this thread how much interest it would generate even though Willi-P actually tried it and posted before I did. I notice alot of people posting pics of they're GS's around the web with winglets on them lately. It's nice to know I was able to contribute something useful on this forum considering how much I've learned from spending (too much) time here.