if you use ribbons they need to have the additional power attached to them so you dont burn out the pci slot on the motherboard.
they usb risers are better in the fact they can be sat somewhere else other than directly above the mobo
plus the circuitry is better than just the ribbons themselves less chance or burning stuff out
not true, i use ribbons all the time with my 1070 and they work perfectly fine, usb risers or powered risers are useless with the h81 pro btc, that come with additional power, they have a reason onyl on MB withotu 2 molex