I used Graphene Matrix RCAs, XLR, Speaker, Coax and AES digital cables when they first came out. They’re very nice for the price, especially on the used market. It was at a time when I wanted something to compare to Synergistic Research Atmosphere UEF Level 3 loom about 4-5 years ago. The performance was nearly identical, and I found that the UEF Level 4 cables surpassed the CT and went back to SR.
While there was a lot of discussion back in the day about 1.5M Coax being better than 1M due to timing and skin effect/noise reduction, it doesn’t really matter these days if you have decent equipment / decent clock in your source. Cables have come a long way with shielding and geometries as well that the length is often better being shorter. I think you’d be better off investing money elsewhere and not on a longer coax cable.