the one which looks cheaper to manufacture

which is definitely the second

If you've read the docs, which I'm not saying anyone is expected to, FTDI tends to put buffers on their outputs. That's what gave it away for me. The little sot-23-5 footprints.

They gave it away by saying the genuine cable was a 234 series (small basic UART) and not a 232 (big ol' 28-pin chip).

You don't need any specialized knowledge, just pick the one that looks "cleaner" and "neater" than the other.

It's sufficient to look at something as basic as the arrangement of cables on the left. The crooked electrical elements on the right are also a big tell.

This works because good—and bad—qualities correlate with each other.