Depends what you want to look at, basically and also how good the mike is - you could have a magnification of x200 with very poor definition! Manufacturers can get away with telling you the magnification but without any requirement to measure the definition ....
x40 would be useful for leps and for looking at flies or beetles to family/genus ... perhaps? It all depends on the quality. You would need to take a few insects with you to the shop and have a look at them - can you
easily make out features such as veins on a fly wing or hairs on a beetle's head? If so, at that price, then it may be worth getting .... Good luck, let us know what happens!
PS: I note that a light-pen is provided - this suggests that there is no integral lighting for the microscope. Might be good to have an independent light source - you can move it round to give the best incidence. However, the light source of a microscope is on a par of importance with its magnification and definition, so, again, try it out as if you were in a dark place rather than a brightly lit shop ....