I have made a similar harness in 3 mm Kernmantle cord, this type of cord has a static tensile strenght of 3000 Lbs! thats about 1360 kg or the weight of small car. U can buy kernmantle in outdoorshops , they use it to make prusik knots. The kernmantle i use is very resiliant to braking( 3000 lbs!) but also against abrasion. They use this stuff as life lines for rockclimbing so they are quit abrasion resistent. I have the same harness as the merc harness and i can carry my Benchmade Nimravus without me noticing it (i tend to forget it) . I am 6.2' and weigh 210 pounds so it might be that the knife just fits me, but this harness disappears under even a white t-shirt. Fantastic design.
Nimravus specs:Blade Length: 4.50",Weight: 6.20oz.,Overall Length: 9.45"
i don't know what CRKT FS u have but the specs of the 2705 seem to be almost the same. If u go to the largest CRKT 2706 this is IMHO to much for the Merc Harness.
hope this will clarify some of your questions.
ps if u can get it direct from Merc harness get it there, it is quit a task to make the harness feel and work right , and with the cost of the kernmantle u might be cheaper and with a lot less hassle( i had to steal two beads from my 7 year old daughter) if u just get the merc harness. Because i live in Europe, and had the cord lying around i copied the design
and made some adjustments myself so the harness is interchangable with my CS Spike, my Spyderco ronin, etc