Yeah, those have been around in CF form for a while. The first one was buggy, the second was less buggy, the third was no less buggy (as in the wi-fi would only work half the time, the memory would get corrupted, etc., etc., etc.) But then they made them in SD form. For some reason, those have all worked fine. So, go for it.
Oh, and about functionality vs. form, Check this out.
I have one, it's a lot more useful than I first thought it would be. It's so friggin tiny! But not everyone has $1600 to spend on a tablet with a 5" screen, so make sure you have a decent comp first. But with a cellular CF card, the U50/U71 can become the most useful productivity / entertainment tool ever.