Mill Production is for 2.5d work, in the sense that you can only import surface models, and extract edges from the surfaces, to create wireframe or profiles and pocket boundaries to machine.
So far as wire frame machining, you can still create 3 axis toolpaths in Mill Production, if you draw them, but this is not the true essence of 3d modelling.
Mill Professional XP gets you into the surface and solid creation and manipulation, as well as automated toolpathing of surfaces and solids.
As I understand it, "Hybrid" modelling means that solids and surfaces can be handled in a similar manner by OneCNC, when it comes time to make automatic toolpaths.
The way I visualize it presently, the surface data is what is of paramount importance to OneCNC. Whether a model is "solid" or not, does not really concern us, the users. A solid is any combination of surfaces that closes in a chunk of 3d space completely, hence the term "watertight model".
Solids can be handier to manipulate than seperate surfaces. When you slice across a solid (in software), the software automatically creates a new surface to close off the cut section. This is like your sawblade creating a new surface when you cut the end off of a 2x4.
However, if you simply cut across a collection of surfaces that are not closed (merged) into a solid, then you end up with an open ended structure, like cutting the end off of a beer can.
However, there are times when it is very difficult to build a software model of an object using only "solid tools" to create it. Sometimes it is far easier to create some surfaces, and then merge them to create the final solid. This is a hybrid type of action. This is just my opinion of what the differences are between a full "solids-only" modeller, and a hybrid modeller.
Anyways, back to what you are planning to purchase: I don't want you to be disappointed because it is not what you were expecting.
"Planar finishing with SMT" is one of the concepts in Mill Professional XP and Mill EXPert. You will not see it in Mill Production. SMT is OneCNC's "Solid Machining Technology" which creates gouge free toolpaths, using the actual information of the modelled surfaces to calculate where the tool may or may not go/fit.
What planar finishing is, is the creation of automatic toolpaths that run back and forth across a 3d surface, something like closely spaced parallel lines, projected onto the surface. The tool simply follows the line in X and/or Y, but the program generates the Z component from the model. This is a common method for finishing curvy molds and such, using a ballnose cutter.
The other main method in Mill Professional XP, is the Z level roughing and finishing. This is like horizontal slices of your part, which are used to create contour-type profiling cuts. This would be similar to what you see in a contour map of the world, where the lines twist and turn all over the place to maintain their fixed level.
These two processes are probably used more than all others, so that is why they are offered in Mill Professional XP. There are other more unique and specialized surface machining functions offered in Mill Expert, that are for people who have particular, yet common to the industry, needs to do special things with molds, such as detect areas that were not yet cleaned up by the previous processes, in order to do "zone machining" in a quick and efficient manner.
I could ramble on, but my fingers are begging me for breath