They do work but only if your CPU/Chipset support enough PCI-e Lanes. Example a Intel 775 Motherboard with a Core 2 Duo can run 6 cards using one of these but you have to turn off almost everything in bios to free enough pci-e lanes to get the 6th card to work.
What about MSI Gaming M5 or Z170 Carbon
Or using m2 to pcie works ?