I had a "Bitchin Betty" installed a few months ago. It is the one which operates off the same sensors as the stall warning and gear alert horns. I have not had it come on due to my inadvertance, but have "tested" it. The voice is such you could not miss it. (After the installation, I had the avionics guy turn the volume down, as it was originally god-awful loud). My belief is that it would take a complete idiot to do a gear up landing with it operating. It has the same level of warning for stalls, and I hear it quite often landing. I think this would also be very hard to ignore unless a pilot was frozen into elevator-up mode trying to avoid an impending crash. I considered the other types that have their own stall sensors, but this one is quite a bit cheaper, and I think it is well worth the cost. My belief is that the original horns are not loud enough to penetrate good headsets, at least to the extent of arousing ones consciousness ot the problem.
Don