Cat A.

What people don't fully understand is that Aliexpress is only the connection between buyer and seller. The site does not directly sell the goods. It is like a Chinese eBay; there are some good sellers and there are some sellers just trying to rip you off.
China is known for basing its products off others ("samples," sent from out of China.). In other words, China is notorious for its counterfeiting culture. They are very good at it. They are very bad at product design.
It is very hard to find real, original products from China. That is why everythig is cheaper; it's just a copy of another version.
Also, regarding product quality; as I stated before, they are more than likely knockoffs. Quality can still be very good. Or it can be very bad.
I would advise you look at the ratings on whatever you're going to buy. I've only ever bought things that have thousands of reviews and at least 4 stars, and I've never had a problem.