My thoughts.
I think that machines are justified
if you couldn't work the muscular structure you wanted to work in
"conventional ways" (barbells)...but some structures are "tweeners" like the triceps...
I think time has proven that the
triceps can be worked best when not
isolated...
Although, I think cablesin this instance is a good choice for triceps, you use the cable as in a pressing action, but that places a lot of stretch on the tricep, so you got to be careful.
Pressing movements are the trick, for arm growth.