A good mirror type or reflecting telescope needs a mirror at least 4 inches in diameter. Imported department store scopes use eyepieces that are .965 inches in diameter that offer dim, severely restricted fields of view. In an astronomical telescope, power usually refers to the magnification that the telescope is capable of. That means that our department store refractor with its 2.4 inch lens should top out at a magnification of 120X. That means that magnifications beyond 120X, while they can be had using the appropriate eyepiece, will not allow you to see more. Instead, the scope will show you a dimmer, fuzzier image.
Magnification is among the least important features of a telescope.
What is important with a telescope is light-gathering power, and that is related to the diameter of the scope's main lens or mirror. The bigger the better. Experienced amateur astronomers typically use lowest powers when observing with their telescopes. You can figure out the power that a given eyepiece can produce by dividing the focal length of the eyepiece into the focal length of the telescope. A 4mm eyepiece included with that scope is useless because it produces excessive and unusable magnification.