On a cross-country tour in 2017, I used SPDs and went down twice when I misread the slope of the ground and unclipped the wrong foot. The loaded bike may have had something to do with that. (I ride mostly with clips and straps, but have also used SPDs extensively over the past 15 years or so.) I suffered one lightly skinned elbow but most of the damage was to my pride.

Not wanting to repeat that, I tried a set of cheapish BMX platform pedals and comfortable hiking shoes on a 900-mile tour of the South this past march. No comfort issues in the course of some 70- and 80-mile days. No loss of efficiency that I could detect.

Speaking of which, is there any actual data on the relative efficiency of flats vs. clips and straps vs. clipless? There may be some small gains, but I would expect them to be very small. I suspect that clips and straps are mostly a C&V signaling device. I guess that's why I still have them on most of my bikes.