Sorry, you're right. I meant they said: "I contacted Macsales.com about their Envoy Pro SX, but they tell me an Intel MacBook 2018 is not going to benefit from PCIe 4.0." Not 3.0.
But they were saying if you use PCIe 4.0, your results will be worse than 3.0 since I have an Intel MacBook Pro 2018.
From what I understand, it's more like you say. It's just that it's not worth the extra cost, but your writing speed might be a little faster.
I think I'll go with the Acasis enclosure after all. It also has USB 4 compatibility at a good price.
Thanks