The entire bottom part came flying down and smashed my foot

As others have said, you have to mind your foot placement while using it because it's easy to drag your foot on the edge outside the belt.

The motor is very weak, so when you walk, the weight of your foot stops the belt for a moment (even at ~120-130 lbs), and the treadmill jerks your foot back as it collects the power to keep going

I wish the belt had some cushion below it, as it hurts my feet.

My feet kept either hitting the front-end of the treadmill or falling off the back end

The treadmill deck is hard plastic (with no cushioning system of any kind), which together with the jerkiness and vibrations make for sore feet