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My guess is that the difference in actual user experience of a system receiving a 923 and one receiving 893 will be negligible. Between the two, I'd choose the one where I get a better deal.

By the time you add the size and weight of a converter box, you should probably just get the Z Cam EVF or the Portkeys OEYE and save money.

It's possible to synthesize all sorts of microphone types/polar patterns, including things like perfectly co-incident stereo pair mics (which are impossible to physically build), from a B-format Ambisonics stream/recording - https://en.wikipedia.org/wiki/Ambisonics#Virtual_microphones - and also produce a binaural stream - https://en.wikipedia.org/wiki/Ambisonics#Decoding I think that post-processing flexibility is the real strength of using a Soundfield microphone for ambient sound recording.

I did a first impressions thing here when I got my H3-VR. It has examples of the auto down mixed binaural output for general city ambience and you can download the original ambisonic files to see the extent of the steering that you can do with them in post if you every wanted to. I think it obviously punches above its weight and even in binaural mode it does add more pickup width outside of the visible frame as well as a certain degree of rear and height cues so for 180 video I think it might do the trick for what you are after without having to do anything in post. The step up would be the Rode Soundfield mic paired with something like the Zoom F6 or even the new H6 Essential but, obviously, you will then need a more elaborate rig versus the diminutive H3VR and, of course, with no down mix you'd have to do that in post.