I’ve personally not raised an issue with single card slots. Sure two are always safer, but I did my first two years with two single slot Fuji bodies so I’m used to a workflow that is as safe as it’s practically possible to be with one slot.
- The highest percentage of photos are taken on my a7III anyway
- Most key moments are taken at multiple focal lengths, so across two different cameras (thanks to the wonderful Holdfast Swagg)
- I backup everything taken so far onto a laptop during the wedding breakfast
- A portable drive containing a backup of all images (from both cameras) goes to my parents’ house on the way home from a wedding
Take the a7III out and replace it with another a6400 and that’s still a pretty reasonable safety net.
So even with a camera with a single slot in my workflow, I’ve got 4 copies of the majority of photos in 2 completely separate locations by midnight on the day of the wedding. I’m sure the biggest risk by far is getting mugged leaving the venue or travelling home in the car after the wedding with all the images in one place (but even then, the laptop is in the boot and the SD cards are in my pocket), as they are single points of failure.