TetraMic owner here. I dig it.
I heard a talk at Moogfest earlier this year about 3D sound by some folks at Virginia Tech. They've put together an enormous hemisphere of speakers on the VA Tech campus called "the Cube", for 3D audio research and performances.
At a demo of a "small" hemispheric system at Moogfest, they had a Core Sound TetraMic sitting on the display table and I asked the engineer, Tanner, whether he liked it or not. He said that it "wasn't the best for localizing sounds". I'm not sure what he thought would be better or how good the TetraMic really is, or how it compares to the Sennheiser version.
This may be as much a comment on 1st order Ambisonic recording and ambisonic playback (that is to say, all tetrahedral single-point ambisonic microphones as sources for their multi-speaker 3D playback arrays) as much as it is about the TetraMic in in particular, in comparison to other 1st order ambisonic microphones. No 1st order Ambisonic microphone can provide the sharp localization of higher-order ambisonic playback common with synthesized soundscapes and those built from panned monophonic elements within a in higher-order environment.
But those are issues which won't really apply to taperssection users of these types of microphones, where the target listening format is 2-channel stereo. In that case, these mics are unmatched due to the unprecedented degree of control they provide the to a recordist afterwards via the ability to point a virtual pair of coincident microphones of any 1st order pattern of their choosing in any direction of their choosing. Some smaller subset of users will use these for recording for multi-channel surround playback. In that case, these mics offer unprecedented convenience, compactness and ease of use. That will in many cases trump ultimate playback quality questions. For ambient quadraphonic location sound recording for film and TV (for use in combination with separately recorded dialog, foley, effects, etc) it can be excellent. Yet for optimal recording of music for surround playback, there is no substitute for non-coincident microphone arrays which use spacing between various microphone elements. That's a basic, inherent limitation of 1st order pickup patterns and higher channel counts. For more than 3 or 4 coincident channels, higher than 1st order polar patterns are required to optimize the pattern overlap. But I'm not aware of other tapers recording for plain vanilla horizontal 5 channel surround playback, much less exotic cubic or hemispheric 3D playback, so the ultimate suitability of these kinds of microphones for high spatial resolution 3D playback isn't going to be relevant to live music tapers.
If you like coincident stereo mics, these things are the ultimate. They work great on stage or at stagelip. Stick it in the right spot (there is no work around for that), and adjust everything afterwards by ear. It doesn't even mater which direction the mic is pointing, as long as it is in the right spot. But you need to be comfortable with adjusting things on the computer afterwards. That blessing of adjust-ability may be more of a curse if you are a taper averse to having to do post-processing.
One thing which differentiates the TetraMic from the SPS2000 or this Sennheiser mic is the calibration Core does which is specific to each microphone. That does a lot to correct for variations between individual capsules, as well as correct the overall response of the microphone. I think Core provides calibration services for Soundfield SPS2000 mic owners now as well. There was some discussion of that and how it corrected inherent deficiencies in the original SPS2000 response over at Gearslutz several years ago, but I've not followed that discussion in depth. Same could be done for the Senn version.
Love to hear the Moogfest and/or VT playback systems, would like even more to play around with them with my recordings. I've never heard true ambisonic playback, and a doubt that many who use these microphone for music recording have either. I am working towards setting up an 8 speaker cubic array, attached to the vertices of a 10' square pop up tent canopy though.