The Canon EOS-M6 got tested by DPreview and DxOmark.
Dpreview conclusion is:
Admittedly, if you’re not already bought into the Canon system, it is hard to ignore direct competitors that often pack in more features for similar money or similar feature for less; the EOS M6 ends up being a ‘premium’ option for those that really want it. Many of those rivals also have better-established lens ranges, if you don’t already have Canon lenses to adapt. But, in the end, if you do really want the EOS M6 you’ll be very happy with it: it’s a great camera in many respects. Even so, the lack of higher-end features combines with that premium price to keep the EOS M6 from earning our highest honors.
DxOmark conclusion is:
For enthusiasts wedded to the Canon system and looking for a small mirrorless camera to use with existing EF-M, EF-S, or EF-mount lenses, the EOS M6, alongside the EOS M5, offers the best features and image quality for a Canon hybrid to date. The compact size is perfect for slipping it into a small day bag for trips out, especially when coupled with the pancake-style 22mm EF-M prime lens. If you’re planning to shoot a lot outdoors in bright light, where glare can be a problem, the omission of a built-in EVF is problematic; this makes the M5 a better choice, but it’s bigger and bulkier. For those not committed to a particular brand, any of the Sony a6xxx-series mirrorless cameras offer the same compact styling as the EOS M6, but with the benefit of a built-in EVF, together with marginally better image quality, in roughly the same price bracket.