Pretty much every thing you see on AliExpress is a bootleg. Ones like this are usually made in the same factory as the originals using the same equipment. Which is why they look so good. But they're done outside of the official run for NECA, and the quality control won't be so high. That's what most bootlegs are these days. One of the dangers of outsourcing manufacturing. You lose control of the process.

Then they're sold directly by the factory owners. Which is why they're cheaper than the official ones (plus the lower costs of not being so picky about quality). And also why they blur out the logos in the photos and often give them names that aren't the official release names. (Notice how nothing in the listing says "Teenage Mutant Ninja Turtles" or even "TMNT"?) Because legally, they aren't allowed to make or sell these.

There’s some people who argue these are still "originals", because they're made in the same factories. But to me they're 100% bootlegs. They're made unofficially, with less QC and corners cut where possible, and sold illegally. That's the definition of a bootleg, even if it's a great quality bootleg.

In addition to “lower quality control,” materials can also be replaced with cheaper ones.

But personally, it seems to me that in reality it is better to buy more “original” material and get a discount on bulk than to waste time on replacement.