i don't get what citronick is saying about "better heat control" but risers are imoprtant to make space between hot gpus, the closer they are together the hotter they get..
quality risers are good, most of my risers from late 2013 are still going strong.
Avoid the molex powered risers or any of the v1 to v5 risers.
Why avoid Molex - the connectors can EASILY handle the needed 75 watts (the actual connectors are rated for about 150 watts IIRC) as long as the WIRING is beefy enough.
Avoid SATA definitely, those connectors aren't rated for more than about 45 watts and WON'T handle the load.
to rslx - if you're willing to wait, your best choice is to buy from the manufacturer(s) direct.