Well, I can see that you have got a round face. Personally, I find people with round face quite cute and attractive to be honest. So, in my mind, butterfly sunglasses are amazing, but I don't think they are confined to slim faces, they also look gorgeous on round faces, as long as you dress well and pay attention to your overall looks. Anyway, you can just go to try them on.
Well, it is hard to say. It all depends on what frames you choose. In your situation, I think you should not wear the square frame for your round face. Maybe you can try the round frame which can make your face look thinner and not so big. As we know that if you don't choose a right frame, you will not look attractive. Also, the colors of the frame play an important role in the image of your face. So next time when you go to the store to choose a pair of glasses, you'd better pay much attention to the two factors. And you also can get some essential information from the professional person. Butterfly sunglasses allow them to be very lightweight while at the same time being both strong and flexible, and also they are very attractive. Just know something more about them and make a right decision.