It really depends on whom you ask about designer sunglasses being worth it or not. Many people will tell you they are and then many people will tell you they are not. It all comes down to priorities. What one person holds dear another may not. Some people believe if you pay a lot of money for designer sunglasses then you have the best but what is the best?
Sure, paying for a name brand you would think would guarantee you a pair of glasses that are made from very good materials and would give you maximum UV protection from the sun. And most likely this is true for many brands. But there are still reputable manufacturers out there that make maximum UV protection sunglasses that are also fashionable and long lasting for budget prices. They just do not have a designer name attached to them.
For the majority of people who do buy sunglasses, a designer name is not important and that is probably because they know they cannot afford them so they look to prices they can afford. The fashion industry is a very fierce industry and in this day and age there are many manufacturers producing sun protective eyewear so it will always be a competitive market. This is good for you the consumer because that means bargains.
If you look around and in particularly online you will find that there are lots of opportunities to find a great looking pair of sunglasses that also offer maximum UV protection. You do not need designer brand names. But of course if you do want a designer pair then you will also find discounted options when looking online.
The important thing is that you find a pair that you like the look of, has high UV protection and is at a price that you can afford. Any product is only worth it if you can afford it.