Thank you for your honest impression. It sounds like according to what you and other reported the player could have been designed extremely well to work with phones in the 32 to 300 ohm range appropriately and that to maximize its performance to be used with TOTL phones except for some other phones like the HD800, the power would be sufficient to last in the upwards of 5-6 hours. Like @Sauntere I would have also liked to hear what TOTL iems/ciems it could have a great synergy with being interested in portability on one hand. The answer from the CEO about not being able to increase the battery runtime does not surprise me. It looks like to be able to enjoy the player longer will require a portable battery pack which with the size and heft of the M will make the stack less portable. Even if they design an amp, portability will be an issue with M due to its relatively larger size and weight. As a desktop unit with USB DAC connectivity then it might be more at home.
Can you tell us what were your criteria as far as functionality of the M is concerned you were interested in and have they been met?