The M1 also has a Virtual Surround function, which in conjunction with Dolby Digital+ and eARC input support are all features that are meant to enhance movie and show watching. If you're a pure music-listener, it means nothing to you, but for people who do watch movies and shows on their M1, they'll have a nicer experience than on a Wiim.
Additionally, and it absolutely amazes me that we've reached page 4 and nobody has mentioned this, but the M1 (and its more affordable sister, the Denon Home Amp) both support DIRAC Live room correction, which is leagues better performing than Wiim RoomFit.
The cost of adding a DIRAC Live license to this amp is a lot less than buying an entire miniDSP Flex plus DIRAC Live license.
If you don't take advantage of DIRAC Live and don't use your system for anything other than music, the M1 is not a great value.
For people who want, "just one box that does it all," this thing truly checks all the boxes. If you're willing to have two or three boxes to do the job, then I guess a miniDSP Flex combined with one of the newer inexpensive class-D amps with ARC input might get you close. I suppose there is also the miniDSP SHD Power, but I don't know if that amp has load-neutral frequency response.
I should not be the one that has to point out also that the room correction functionality easily trumps SINAD differences between this amp and others of lesser or similar cost that don't have DIRAC Live.
If you really believe room correction doesn't improve your sound, well I'm happy you're blessed with such a perfect, dedicated listening room.