Personally, I'm against sandals for biking shoes. I tend to kick things when walking and if I had sandals, I would injure my toes. I want my toes protected. But I know people who use sandals for biking.
Hot spots can be caused by a flexible sole and small pressure point such as the cleat. Some people notice it, others don't. Some people it bothers a lot, others it goes away quickly and does not hamper them at all.
When I ride with my cheap, flexible Specialized mountain bike shoes, and SPD pedals, I get a hot spot after about 50 miles. Doesn't cause me to stop riding or make me limp. With my expensive, stiff Carnac mountain bike shoes, I get a hot spot after about 75 miles. Until I moved the cleat back so I am now riding less on the ball of the foot and more on the flat part of the foot behind the ball.
The soles on Shimano sandals would fall more on the flexible end of bike shoes.
My mother used Speedplay Frog pedals to ride across the US in 2000. I did not hear any complaints so I assume they are good pedals.