Can't believe I'm seeing Ali Express compared to Amazon, and apparently in a favorable way.
Ali Express is overrun with sellers with identical listings, but the quality may vary greatly between them. You will only know when you receive the item. It's not uncommon to receive something that looks totally different than the listing images.
Shipping something back on Ali Express is basically a total no-go. They get killer discounts on shipping to the US. Shipping something back to China is probably going to be more expensive than the product. With Amazon it is cheap or free to return things.
Sorting by price on Ali Express is totally broken, because sellers can list a variation with the lowest price that is never available. This impossible-to-get lowest price is taken into consideration by the sort.
People complain that sometimes Prime is 3 or 4 day shipping instead of actually 2 days. Ali Express is 2 weeks minimum. Probably 50% of the things I've ordered have taken 1+ month. Some things take 2 months. Some things never arrive at all.
All that said, I still use Ali Express. It's great for small, cheap and generic items. I know what I'm getting into, and I accept the risks. There is no way it could replace Amazon.
If you knew nothing about Amazon and only learned about it from HN comments you would think it was basically the Mos Eisley Cantina. The real eCommerce Mos Eisley Cantina is Ali Express.
Shopping on Amazon is still cheap and convenient. Maybe not if you consistently buy things that are exorbitant to ship like ping pong tables or 6 foot ladders, but most people buy items that could fit in a shoe box.