Just bought a Viltrox EF-M2 speedbooster for my Canon M5. It should arrive Wed., Dec. 19th. Do any of you have this adapter or similar, and have you seen any variation above or below your expectations? Several reviews stated image quality is not compromised a lot. The two lenses I was most interested to use with it on the M5 the 85mm 1.2 ii and 16-35mm f/4 IS. I also considered the Rokinon 12mm f/2 but apparently it's more like an 18mm on the M5, and unless I misunderstood, 16-35mm with the Viltrox adapter should remain closer to 16-35mm. So I opted for the adapter rather than an extra (manual) lens.
The image quality is decent. A question mark lurked from the M5 screen, but once in Lightroom, the photos were as good as hoped for. I didn't buy this for top-notch images, but extra versatility when I want to use the M5 as an extra body to get a few more photos that could be printed 5 x 7 to 8 x 10
Here is the Canon M5 & Canon 85mm 1.2 ii shot at f/1.0