Chances of getting a two year tourist visa ?

Hello! I was wondering what were the chances of actually getting the whole two years when you pay for the two year visa instead of the six month visitor one. Not intending to stay longer than six months at any point, but want multiple entries over a two year period. I just don’t want to pay the extra cash if they’re not going to give me the whole two years, as I’ve heard the two year thing is more of a suggestion than a certain thing. I have enough of a reason to go back to my country of residence (doing my masters), can prove I have enough funds to support myself through my studies, and my sponsor is more than comfortable enough to pay for every part of my stay. If you have any experience with this any input is welcome, thank you.