I would NEVER term these whips FMC -- they are listed assemblies -- like MC.
Whereas one can re-pull conductors in FMC -- such is entirely impossible for these assemblies.
While longer whips -- evidently -- are possible -- in our jobs the typical M/S were not all that far apart.
Their great appeal is energy efficiency for A/B switching in a commercial setting.
I've never seen any AHJ go for the 4.5' rule -- they use the MC 6' standard, instead.
Lithonia's ReLoc is another listed assembly -- which always gets treated like it's MC.
ReLoc is available in very long distances -- and if you're willing to pay-up -- Lithonia will custom manufacture to your spec's. You'd better have the volume budget of Walmart, though.
While ReLoc saves labor, big time, it is pricy. It's plug & play nature requires no competence from the scissor man. It also eliminates j-boxes like crazy.
