I can imagine what you mean. But take my word. In a helmet the voice sound a lot easier to the ear than on a laptop. It is calm, no sharp tones, very clear to understand in noisey (wind) conditions.
The sharp tones in the default TTS engine of Android is for me the biggest problem.
Other benefit of the voice i made a sample of. It is louder than the default voices of Android.
Because it is louder it evens out (almost) the volume levels differences between... let say Spotify or online radio apps.
When i listen to online radio on a decent volume level with my prefered app. The volume of the MRA directions has a very low volume level. I almost cannot hear what the directions are.
This is not perse a MRA problem but inherent to the Google TTS Engine. Other navigation apps which use the Google TTS engine have the same problem.
So it would be nice if MRA could fix this also somehow