Quite entertainingly you can use both webcams simultaneously. Personally I think the build quality of the logitech one is higher, but the automatic white balance kicks in with the Technika one resulting in more visually appealing display (I haven't tested with windows, but I suspect the white balance kicks in there for the logitech).
Overall, I think I personally prefer the technika as a result since for me on my preferred platform, it just works. I'm very tempted now to see if I can create some python bindings for this (which would work with both cameras under linux) since it'd be nice to incorporate a video display into our Kamaelia based whiteboarding app. :-) (Hmm, reminds me, I should put the Kamaelia Whiteboard tutorial from Linux Format online now that the issue with the article in has gone off sale).