What are the wires used for the SFF8639 (U.2) transfer extension cable? What is the difference?

What are the wires used for the SFF8639 (U.2) transfer extension cable? What is the difference?

1. PCIe high-speed dedicated line
Bus supports M.2(M-key) or PCIe x4
Maximum bandwidth PCIe 3.0 x4
The longest cable length is 5-100 cm (customizable)
Hardware structure The welding points are reinforced and tightened, and the core wire and power core wire are sufficient. The NVME SSD is directly inserted into the motherboard through the PCIe high-speed cable, with good compatibility.
2. SFF-8643 adapter cable
Bus support SFF-8643 (add M2 board)
Maximum bandwidth PCIe 3.0 x4
Maximum cable length 35- -60 cm (fixed length)
Hardware structure The core wire and the connector are integrally formed, and the M.2/PCIe secondary connection is purchased. It is easy to cause signal attenuation.
3. PCIe adapter board
Bus supports PCIe x4 (full height)
Maximum bandwidth PCIe 3.0 x4
Maximum wire length PCBA wireless length

Hardware structure No wire design, large mechanism restrictions, no support for small chassis.