Good morning,
At the risk of appearing a luddite, are you totally dismissing Toe Clips and straps?
If you have never used them, I reckon that there are four ways to use them but my loss number are very approximate.
Cycling shoes with shoe plates/quill pedals and straps fully done up.
Loss To Clipless: 0%
This is madness nowadays, it was the old racers' system and it is a far worse solution for public roads and much more dangerous than any clipless system. It is also very difficult to buy shoe plates anyway.
MTB cycling shoes and straps fully done.
Loss To Clipless: 5%-10%
A lot of the benefits of clipless and can be chosen for certain parts of the ride, but you do need to grow the confidence to reach down and release the straps. Oddly I feel totally comfortable doing this but really stressed with SPD!
MTB cycling shoes and straps almost done up.
Loss To Clipless: 10%
This takes practice, if you can get the straps done up so that the foot can
just enter and leave the clips you get a lot of the benefits of clips. By just I mean that if you try to pull up out of the saddle on a climb the shoe moves off the pedal by a few mm and then the clip and strap retain the foot.
MTB cycling shoes and straps fully undone.
Loss To Clipless: 20%
This has the benefit of keeping your feet in the right position on the pedals, which can avoid discomfort that is a result of foot slipping backwards and pedalling with the sole of the foot.
The point about MTB shoes is that they usually have soles that provide a little bit of anchorage themselves.
I recently gave SPD another go, for about 1,000 miles and was so relieved when I stopped and went back to platforms or clips/straps. It's tempting to believe that the whole world rides clipless and you would be odd if you didn't.
Bye
Ian