Compression fittings fit inside and outside and clamp the tube between them. Have you ever used a compression fitting in your life? I'm not super concerned with price, and from what I looked up, if I swapped two compression fittings for silver ones, it would equal the cost of a killcoil...
While I may be new to watercooling myself I have worked with compression fittings on chemistry analyzers and seen the results of what happens after you have water flow passing through tubing.
WARNING WALL OF TEXT(but theres good information in it)
Initally everything will be fine and you will gain the same benefits as the kill coil. Over time you will recieve less benefit from the silver plating because silver is a soft metal and will erode the plating as water flows across the plated surface. Things should continue to be fine until you perform a coolant change and flush your system because then all the dissolved silver in the coolant has been removed. Plating is most commonly done by electroplating, which leaves only a thin layer of the desired metal on the outer surface. Once that plating has eroded away, which you would only realize if you were undoing and checking the interior surfaces when you perform a system flush, you no longer benefit from those formerly plated surfaces.
Fortunately the fitting you linked is brass underneath and shouldn't cause any problems unless you have aluminum in your loop. See the sticky for information on galvanic corrosion.
In short its your call on whether or not to use silver plated fitting instead fo a kill coil, just be aware that electroplating is not perfect and may leave exposed areas of brass. Personally I would just use the kill coils and not wonder about the internal surface of fitting with every fluid change.
One last variable...the solubility of silver in whatever coolant you are using, it probably doesnt matter and you probably wont be able to find that information without doing a chemical analysis.