Two card slots just saved my project today. I shot for 3hrs in the scorching FL heat at a project site that was a 1.5hr roundtrip drive to create footage with a new client after weeks of coordination and schedule planning; and captured photography images that would be very difficult if not impossible to recreate since we were working with animals; and when I got home the SanDisk Extreme CFExpress card in the R5 stated it had no useable file system and not a single image had been recorded to it.
I had formatted the card before the shoot, the R5 gave absolutely no indication that one of the cards wasn't working, and yet nothing was written to the CFExpress card (or it got corrupted somehow after the shoot on the way home); that would have been a total loss of 1600 images, a refund of the client's money, and definitely a lost future client if I had only had a single card slot. I am already working with the client to shoot a few different promo videos and more photoshoots with them in the future so this would have been a pretty major loss. In my close to 20yrs of shooting I've never had this happen.
At the moment I don't know what to think; is there a bug in the R5 where it corrupted the file system for the CFE card, or did the CFE card have a problem and the R5 saved the day by continuing to operate flawlessly with the SD card. Regardless of which scenario happened, I now know the R5 won't tell you when one card is not working, it will also keep working with the second card, and I also know I was right to never buy an A camera (other than drones) with a single card slot.