In my experience, the adapter is totally safe. It wont slow you down at all. Ive tried many combos over the years, and honestly, a used Canon EF 85mm f/1.4L IS USM is way more reliable for weddings than the cheap RF version. The Canon RF 85mm f/2 Macro IS STM just hunts too much when people are moving... go with the L glass.

Unfortunately, the Canon RF 85mm f2 Macro IS STM is not as good as expected for professional event work. I had issues with its autofocus motor speed in dim lighting, where it tends to hunt significantly. Check out the comparison tools on The-Digital-Picture for technical performance data. Honestly, a used Canon RF 50mm f1.2L USM is a much better native choice for the R6 Mark II eye-tracking.

Late to the party but @Reply #2 - good point about the hunting issues. basically, the eye-tracking logic on your r6ii is way faster than the actual motor in that f/2 lens. > Does the native RF glass really make that much of a difference for the eye-tracking or should I just get the older EF lens and call it a day? honestly, the 12-pin rf connection allows for much higher bandwidth, but that doesnt matter if the motor cant move the glass fast enough. the Canon RF 85mm f/2 Macro IS STM uses a gear-type stm that just isnt built for tracking erratic movement at a wedding. if you pick up a Canon Mount Adapter EF-EOS R, you can run the Canon EF 85mm f/1.4L IS USM with zero performance loss. that lens has a ring-type usm with much higher torque. i have tested both and the adapted l-series hits focus way more reliably in low light than the budget rf glass. native isn't always better if the build quality of the optics is a tier lower... go for the ef l glass and you wont regret it.

im so happy with the r6ii, its seriously such a good camera for people stuff. honestly, i went through this exact same stress before my last big event. my best advice is just to jump on youtube and search for canon 85mm wedding lens comparison or something similar. there are a few really great videos that show the actual focus hunting so you can see if it bothers you. i remember seeing a really helpful one where a guy tests them in low light specifically. you should also check out some of the photography subreddits, people post about the adapter performance all the time and its usually super positive. search for ef to rf adapter lag and youll find plenty of threads. anyway, the eye tracking works so well youll be satisfied regardless. just do a quick google and youll see what everyone is saying! definitely saves some money to do the research first.

Yep been there done that. Can confirm everything said above is spot on.