I'm wondering if using normal shoes with these certain pedals will be inefficient? Also, do clipless SPD mountain bike pedals have a normal flat side so that you can use it with normal shoes?
Nope, you need clipless shoes with SPD compatible cleats. There are pedals with cages or platforms around outside so you can use normal shoes or clip in. My favorite pedals are Crank Brothers Mallets. There are also plastic inserts but I don't think those are meant to be used long term.
