It's perfectly reasonable, actually, desirable, to model mechanically separate parts of an object as separate parts of your mesh. So the junction between the steel section and the ridged handgrip would be fine as separate mesh sections. Even so, in this case, I would probably duplicate the lower end of the top section and use the duplicate as the upper end of the bottom section, if I wanted a match.
If you're looking to reproduce your reference, though, there will need to be continuity of shading and texture over the junction within the steel section as it shows in your model. In other words, the meshes will need to be merged at some point, or at least have exactly matching normals where the two parts meet.
In order to achieve that, the underlying topology of the two halves must match, vertex-for-vertex, before the effect of any modifiers, unless you want to commit yourself to a ton of work.
Slightly beside this point, it's often possible for subdivision to 'rescue' a mesh. The un-subdivided mesh can be tortured, stretching in a way wildly dissimilar from the final object, and yet produce reasonable-looking curvatures when subdivided. This will almost always cause trouble, and create work. In those cases, there is always a better basic mesh.