I have used this site many many times for several years now. The PROS: you can find pretty much anything and for a way cheaper price then Amazon or anywhere else. (Besides maybe the dollar store) CONS: it takes a pretty long time to arrive in the US so be patient and order with plenty of time to wait (most of the time a month or more).
When buying cheap you can't expect the quality to be of the highest quality no matter where you shop, so be prepared for some things to to have some defects.
I have only ordered things that it wouldn't matter is there were some defects, like some lingire for my web camming. Some of those came with weak stitching that I had to restitch myself but it then that was perfect for what I wanted, or to small because they have smaller sizes then American sizes.
I have also ordered things like Barbie toys and accessories, which again I was shopping for cheap (because it's for a 2 year old that might not even play with it but I bought it to see if they would like those things) and everything I received was actually what was expected (so far, still waiting on about 12 more orders).
The worst thing in my opinion is how long it takes to get here, and the tracking system isn't the best but I can understand and deal with that. I recently had an issue with a seller who didn't ship and closed my order. That seller did not respond to a single one of my inquires which pissed me off. I also didn't see when my refund came since they give you a wide range of days or will come. But I contacted the live 24 hour help and they told me when the refund was issued and I was able to look at my bank statements and find it after that.
Honestly I have found allot of exact same products and quality on Amazon or other places for at least twice the price on some things so don't rule out Ali Express and automatically go to Amazon.
Over all I would highly recommend Ali Express, just a little advice: 1. Don't expect the highest quality and best fit. Shop in person to get a good fit and don't shop cheap if you want the highest quality. 2 be patient it will take a while to get to you. 3 always make sure you check the reviews, ratings, and number of orders to help ensure you will get what you are expecting and a honest reliable seller, just like you should on Amazon, or eBay etc