(see the video below) The Rapid  H4 FLEX NEXT> (Rapid R2R) is the only Flying Probe on the market able to test the Flex-PCB produced in a big REEL. In order to minimize the cost and increase the productivity, some high-volume Flex-PCBs manufacturers have installed lines specifically intended for the production of circuits in continuous reel web (reel to reel). Seica has Designed the new system RAPID H4 FLEX  for flex PCBs with a dedicated vacuum plate in the test area to minimize board warpage for the extremely thin flex circuits. This is Seica response to the constant demand for testing FLEX PCBs, which are rapidly spreading around the consumer electronics, automotive, medical, smart home industries and others. These are designed to fit into small areas with bending improving the miniaturization process and the high-density mounting design.
https://globalsmt.net/technology_news/seica-announces-new-video-for-rapid-h4-flex-prober/
https://news.thomasnet.com/companystory/seica-announces-new-video-for-rapid-h4-flex-prober-40037815