They have a 'one way' design with 16 pads at the Raspberry Pi 5 end and 18 pins at the NVMe Base end to prevent incorrect installation.
They are designed for PCIe Gen 3 speeds and support Gen 2 perfectly fine also.

PCIe GUIDe

The straight 49mm PCIe Flex (This cable) is an extended cable for use with NVME Base Duo, giving you additional mounting options whilst still remaining within spec.
The 50mm PCIe Pipe adds some length, while remaining in-spec so you can mount your NVMe Base more comfortably around an existing case. It allows for a wider range of mechanical setups and might also be handy if you want to mount your Base on top/alongside your RPi 5.