I guess you need to define for yourself what it is that constitutes getting what you paid for. Consider that technical engineering perfection does not always align with the subjective use and pleasure you get from a device. In the end will you listen to the M15 or will you measure it?
Given that you will listen to it are you willing to accept the listening impressions of literally hundreds of users and reviewers who really like the M15 and have experience with other devices? Clearly you know that there exists a chance that the M15 will have measurement issues, but you also must know that that is true for every single device that hasn't been measured. For all you know unless your desktop rig has been measured it could be worse than the M15.
We have seen that even very well regarded expensive gear across all manufacturers has produced measurement duds and busts, yet still subjectively been enjoyed. So again, given that all gear out there is likely to have some measurement issues, in particular DAPs which are tasked with doing so much in such a small footprint, are you interested in listening to music or simply looking at technical data? Amir is clear that in many cases the technical issues he reveals will not translate to audible issues, or if so, in very specific cases. Are you willing to buy nothing simply because it may have inaudible flaws? I would bet that the majority of DAPs would have some pretty interesting measured results.
I am not challenging you as there is no right or wrong. I am merely suggesting that there are two very valid perspectives. All else being equal I absolutely prefer the devices that I buy to be technically competent, but I am also being realistic and accepting that there will almost always be some kind of compromise that I need consider. A DAP is a hyper-complex device, essentially an entire audio system that you can hold in the palm of your hand, and often tasked with also being asked to be a standalone DAC or amp. Tall order to fill so again I ask, if the DAP is widely regarded as sounding very good, has a solid user interface what level of technical measurement compromises are reasonable to accept? If we wait for the perfect measuring DAP that is also a well designed device from a usability perspective, not sure that is likely. I could be wrong of course, but I follow many DAP threads and it is very common to read of great technical devices with crappy user interfaces or devices with a great UI, but not as technically competent. What trade off are you unwilling to make? What measurements specifically must the M15 adhere to for you?
Again, I am asking this not to challenge, but more of a thought experiment. I am actually curious to learn what it is that you most fear will be wrong with the M15 and what measurement thresholds for the criterion you will look at.