Products which remove the sulphur deposits resulting from oxidation and leave unoxidized vulcanite unaffected will ultimately leave microscopic pits in the surface which were previously filled with sulphur. This is because at a microscopic level, oxidation does not happen evenly across the surface. Georged's explanation of this earlier is superb.
Once deoxidized by chemical means, the vulcanite is like a wooden board freshly cut at the sawmill. Yes, it's fairly smooth, but there is little argument that sanding with progressively finer grades of sandpaper or planing with a sharp blade will make the surface even smoother. These methods do not smooth the wood by flattening or compressing the material, but by removing material which forms tiny ridges until a uniform surface is achieved.
I think which side of the "It's Shiny" fence you land on is dependent upon your personal standards for the condition of your vulcanite stems.
If you just want your stems black and free of ugly, bitter oxidation, and are unconcerned about how shiny or smooth they are, then a quality chemical deoxidizer sounds like a great, low-effort solution.
If you like them blacker and glossier, then chemically removing the oxidized material from the surface and applying something like mineral oil to temporarily deepen the color and provide a bit of shine and protection is perfectly adequate.
If you like them even shinier, then adding an intermediate step of buffing the stem before oiling will get you there. Another option is to use a polish, like the one sold by the manufacturer of the deoxidizer.
If you like them to be like-new smooth, shiny, and deep black as I do, then the reality is that all products which remove surface oxidation while leaving vulcanite unaffected will be relatively useless. In order to achieve a deep black and brilliantly shiny and smooth surface, the surface must be free of the microscopic pits formerly occupied by sulphur left behind by oxidation. This means removing the unoxidized vulcanite that surrounds those pits so that the outer surface of the stem is evenly unoxidized rubber which was below the level of the pits. This is achieved only by abrading the entire surface. So, using a product which removes the oxidation while leaving behind microscopic pits doesn't help very much. For me, that would be a wasted step since sanding will simultaneously remove both the sulphur deposits and unoxidized rubber which surrounds those deposits. There may be an argument for using an oxidation remover for places where sanding is more challenging, like right behind the button.