For what it's worth, before clipless was invented, I had shoes with slotted cleats but I wore them very rarely. Being strapped in was too scary for me. I found a compromise where I would tighten only my left strap so I could remove my right foot when I needed, including emergencies. The problem was that I couldn't pull up or back very hard, because my right foot would come out. As a result, I pedaled with unequal pressure.

Clipless is wonderful. It's actually easier to get in and out than toe clips. And pedaling efficiency is greater. In my observation, adding toe clips to pedals allowed me to shift up one gear, maintain my cadence and go that much faster. I guess I'm talking about 15%, because I think that's how far apart my gears are. 15% sounds a bit unrealistic, but it feels that way. And changing from toe clips to clipless cleats gave me another boost of the same size!