Do MTB pedals make a difference?
Yes.
MTB flat pedals use a much broader platform. The platform has traction pins located at specific parts of the pedal that stop your foot from sliding.
Keep in mind that mountain biking is tough on components.
So, the construction of MTB flat pedals are more robust than your average recreational pedal.
The platform is often 1-piece. The bearings are better quality and the axle is stronger.
If you're preference is to clip-in:
Clipless MTB pedals will deliver a locked-in feel. The advantage here is you get to take advantage of the pulling phase of the pedal stroke; (slightly) increasing efficiency.
The second, more noticeable advantage is for fast, aggressive riders.
Your feet are more stable as you're riding through rock gardens, tree root sections and over jumps.
What pedals should I use for mountain biking?
If you're starting out, we'd suggest flat pedals paired with proper flat pedal shoes.
These are safer because you can step-off the platform quickly to stabilise and balance.
There really isn't much of a loss in efficiency compared with clipless SPD pedals.
It's all about your pedalling technique.
If your bike skills are good but you're having issues with feet sliding off the pedals, or just want a more secure feeling to the bike then Clipless SPD will be the answer.
It's worth noting though that Shimano does use a Light Action pedal.
Light action pedals are a safe option for riders new to clipless pedals; they make clipping-in and clipping-out so much easier and quicker.