Besides the image will be very dim and shaky with the poor quality mounts these telescopes have. Luckily, hardly anyone has need of that much power. I prefer a smaller sharp image to a big fuzzy one anyway. Most astronomical objects are dim, so the bigger the aperture the better in seeing these dim objects. In fact most telescopic observing is done with the lowest available magnification.
High power is needed for viewing the details of planets and for splitting double stars.
The magnification of a telescope is calculated by dividing the focal length of the objective by that of the eyepiece. So a 900 mm objective with a 12 mm eyepiece gives 75 power. The longer the focal length of the eyepiece, the lower the power. To make things more complex, there are a wide range of eyepiece designs from cheap to expensive. In this short article, all I can say is that you get what you pay for.