Interesting question! I don’t know what the answers, but some thoughts:
This link may be helpful, because it describes what all the different feature do: https://www.phonakpro.com/content/dam/phonakpro/gc_us/en/products_solutions/hearing_aid/audeo-lumity/documents/PH_Insight_SmartSpeech_210x297_EN_V1.00_028-2448-02.pdf
Speech in Loud Noise is a program that both the I90 and I70 have. The only difference is that with the I90, it’s part of AutoSense and will activate automatically when the noise threshold is crossed. With the I70, you’ll have to activate and deactivate it manually. That program (and I think to a lesser extent Speech in Noise) relies heavily or entirely on directional beamforming that’s based on the direction your head is facing. It focuses on a cone in front of your face and tries to screen out noise originating outside that cone. Only using one aid shouldn’t interfere with it knowing which way you’re facing, because it will know which ear it’s in. But with only one microphone rather than two, I wouldn’t expect it to be able to figure out a sound’s direction very effectively, so it won’t know what originated within the cone and what didn’t.
SpeechSensor recognizes the direction of the dominant source of speech and automatically focuses on that direction, even if it’s behind you or to the side. IIRC, this was only available in the Calm program for Lumity, but I don’t know about Infinio. I would expect a solo aid to do just fine at recognizing whether a sound is speech, but terribly at recognizing its direction.
Speech Enhancer is the one feature I think might still work fine here. All it does is recognize when a quiet sound is speech, then boost the volume of soft speech but not soft non-speech. It doesn’t sound like it relies on directionality at all, so a solo aid could probably do it just fine.
