Canon RF 16mm f2.8 STM lens Review
This is a compact size ultra wide angle lens. It is sharp in center. It never gets sharp in the extreme corners where the image quality remains a bit mushy. It relies on software corrections. I hesitantly recommend the lens with the caveat you are fine with the extreme corners being not sharp. Extreme corner sharpness is usually critical for realty and landscape photography.
If you shoot raw - you will have to use a capable raw editor such as the Canon DPP. I use DXO PL 4. I find DXO does provide a much wider rendering as compared to Canon DPP4. It is somewhere between 14 to 15mm rendering when the RAW files are processed in DXO PL. DXO corrects the distortion, the strong chromatic aberration, and severe vignetting in the RAW images rather well.
Who is this lens good for in my opinion? I use it as a throw in the bag lens when primary shooting objective for that day is birding. It is tiny and hence throw in the bag. I don't vlog - I however see it as a decent option for vloggers. It may be handy UWA if you are a photographer who never shoots UWA and wants to get into it and test the waters first.
Not recommended for landscape and realty photographers for whom the extreme corner sharpness matters. This lens won't delivery that at any aperture. Ff you are using the R or RP camera, this lens does not have IS so try to keep the shutter speed 1/16 or higher and a steady hand.
Reasonably fast and accurate AF
Provides a wider perspective than 16mm and can squeeze 14.5mm perspective (approx) with DXO PL
Things to consider
Not weather sealed
Extreme corner never gets sharp at any aperture
Severe CA and distortion and vignetting in uncorrected RAW files. This though can be mitigated by a capable RAW editor