We don't have 12$ shin guards around here, so I couldn't compare...
Of course, you usually have to pay for quality, but it doesn't mean you have to pay extra!
The big companies have lots of ad and sponsorship to cover so there's the extra.
I actually own the ones ones I showed you. Yes, they are warm for summer and I would sweat under, but comfy in winter protecting my knees from cooler wind. I wear mine under my jeans, they are low profile and almost unnoticeable.
I figure it is better to sweat a bit than wear shorts and flip-flops!
In the heat of summer, I usually have mesh pants, so those breathe much better.
Also depends if you will be wearing shoes or boots. You need shorter shin pads if you plan on wearing boots, and longer ones for added protection if you wear shoes.
