I make my own ribbon cables and I also pay a company in China to make them for me. Its worth it to me because I end up dealing with so many problems that end up connector related. Ie I put in a new WPC89 MPU but one lamp row, one solenoid, and some GI lamps don't work. Back and forth, oops the ribbon cable had a data bit broke off.

I am not sure about the testers, I think they would only really be good at checking old cables, but the issues with ribbons can be intermittent. I have had zero problems with any new ribbon cable from China or the ones I make. They old ones do go bad over time when the wires rip, pull away from the crimps, or the contacts just go to hell. The new ones take so much more insertion/removal force than a 30 year old one.

The only ones I make by hand are the 34p ones for WPC games that goes from MPU to fliptronic to sound to display. The place in China i've used a couple times does not want to do ribbons with more than two connectors crimped on for whatever reason. I found spools of ribbon on Amazon for pretty cheap. The basic crimper on Amazon is OK too, but easy to do crooked crimps. I need to setup something to keep the crimper and wire aligned right.

Pretty sure I go the crimp on bits for stupid cheap from LCSC. FC-XX is the part number.. FC-34 for 34pin.

I have the tester and I've used it a few times to confirm a suspected or intermittent issue with flaky ribbon cables, but that's about it.