The differences are very apparent when you compare them side by side.
RMJ - ATC , better fit and finish, less flex in the handle, better sheath, better edge geometry for cutting, better purchase/grip
ATC VTAC - Better for general demolition of things, obtuse edge with a convex secondary, more flex in the handle, came in a few different sheath types - the good sheaths were made by spec ops brand.
Both are great for throwing, both are nearly indestructible, Both are 1060 steel.
The ATC VTAC takes a little work to get sharp but it could hack through cinder blocks if need be.
I’ve had the opportunity to own about 5 of the VTAC models, all had differences in edge thickness, hand sharpened.
I’ve had about 4 of the model 1 and they were pretty much identical, besides the 1 with hickory handle.