It states in the Product Description:
Occasionally, the bobbin case may become loose and move freely within the throat of the machine, or it may pop out. This can be remedied by re-aligning the bobbin. The repositioning of the bobbin can be done by hand by turning it and gently shaking back and forth. If the bobbin is stuck and you are not able to turn it or reposition it by hand, a screwdriver can be used gently to lift it in order to reposition correctly and place the black knob to the left side of the white plastic edge. Please be careful to gently lift the plastic edge with the screwdriver, applying too much pressure can make the plastic edge break.
That would make me hesitant to buy it - if they have to explain how to fix a defect with the machine in the actual product description, then that bobbin is going to be popping out every time you use it.