I can say from my experience, as long as you go with 6-pin PCI-E risers, you shouldn't have a problem. The ver 006C have a good build quality with four capacitors and a voltage regulator. I have 20+ 6-pin PCI-E risers ver 006C that were bought from different sources and have been in use 24/7 from early this year. I haven't had any issues other than the soldering on the x1 PCI-E connectors needs to be filed down and covered with electrical tape so that it doesn't short out with boards like the ASRock H110 Pro BTC+ that have the PCI-E slots too close together.
If you are willing to wait about 3 weeks, suppliers from China on Aliexpress and eBay will have the best pricing. I'm currently waiting on a batch of the new improved ver 008C 6-pin PCI-E risers that claim a reduced power consumption vs the 006C version. I have ordered from this supplier before and have not had any problems.
https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20171216220616&SearchText=TISHRIC+VER008C+
