I have single-sided hearing loss which happened suddenly in 2008 when I turned forty years old (SSNHL, unexplained cause). Severe loss in the right ear; normal hearing in left ear. I was fitted with a single HA (phonak exelia) in my affected ear, and it was helpful but not great for me. Especially in noisy situations; it’s amazing the degree to which the brain requires two “synchronized” ears to distinguish conversation in a noisy room! Amplifying sound in my bad ear wasn’t blending properly with my unassisted good ear; it mostly just added to the cacophony. I bought an FM external mic (circa 2008) for my conversation partners to to wear around their necks at dinner parties; it helped somewhat, but because it was sending the amplified signal to my bad ear, it wasn’t great, and it ended up gathering dust in a drawer.
Eventually, I wore my HA less and less, until I was barely ever using it. Ten years later, I went to see a great audi (Wes Nakamura at Family HA Center in Honolulu) and he told me that my lack of using a HA was probably contributing to my declining ability to distinguish words on my right side-- the neural circuitry for language processing essentially shuts down when you don’t exercise it. “Use it or lose it”, he told me. He listened to my complaints about the HA experience, and he had an interesting idea: why not try a pair instead of just one? Perhaps amplification in my good ear might help? Especially with today’s fancy HAs that can use triangulation of multiple mics and sophisticated signal processing to block out ambient noise and amplify specific voices-- which is not possible with a single HA. And perhaps they have the ability to transmit sound from one side to the other, like a CROS or BICROS…
I was very skeptical, but I agreed to try it: a pair of Marvel Audeo M-90-Rs. We used a smaller dome on the good side, so it would occlude less, and of course, the amplification levels are much lower on the good side. The result: it has made a HUGE difference for me! In programs like “Speech in Loud Noise” and “Speech in 360 - Right”, the mic on the bad side amplifies sound in that ear, but also sends its signal to the HA on the good side, where it mixes with the good side’s own mic feed. For me, the result is much better than with only a single HA. Someone talking to me on my bad side gets amplified in my good ear, just like a CROS or BICROS system.
And when I tried the latest external directional mic technology-- the Roger Select, a half-dollar sized disk that sits on the table or clips to a collar, with 6 mics in a circle that can be individually activated by touching them, sending sound to my good ear was truly astonishing! I could hear my conversation partners perfectly in a noisy restaurant! Unfortunately the M-90’s aren’t yet compatible with the Roger Select, so I only experienced them with a different model of trial HAs, but I’ll be buying the Select as soon as it becomes compatible (hopefully this November).
As an added bonus, the M-90s work like a bluetooth headset with my Android phone; I can take calls and listen to music. As others have posted here: the M90 sound quality on music streaming is absolutely fantastic. Having normal hearing in one ear allows me to enjoy high-fidelity sound, and I can honestly say that I prefer listening to music with my M-90s over my Bose and Etymotics. They have an incredibly detailed, wide soundstage. I had to fine-tune the levels using the Phonak fitting software, but after I got those right, I’ve achieved music nirvana.
I’m sharing this with the hope that others with SSNHL might benefit from trying two HAs. And to remind everyone of how important it is to have a good audi! I can’t thank Wes enough! It really has profoundly improved my life. After barely wearing my single HA for the majority of the past decade, I now wear my beloved M-90s every waking hour 
Does anyone else have a similar experience?