I would like to throw my hat in the primary/secondary bevel discussion.

If anyone has not read "The Complete Guide to Sharpening" by Leonard Lee it is a great book in understanding the aspects and theory of sharpening. Granted it doesn't talk about razor sharpening since it is mainly a book on sharpening woodworking tools but the concepts are solid.

Leonard talks about the double bevel in pretty good detail. Many times it is coveted because of the strength it adds to the edge, reducing sharpening time and also the cutting ability of the secondary bevel is increased because of the primary bevel given that the width of the secondary bevel is shorter than the object being cut.

Now when working with woodworking tools the technique for producing the double bevel is say you want a 25° angle, your primary will be either 23° or 24° using only a course stone and then add the remaining degrees after the primary bevel is set and it is only this secondary bevel you hone to the finishing stone. This as long as the width of the secondary bevel is shorter than the item being cut will produce an edge that has the strength of a 25° bevel but will have the finer cutting ability of an edge as if it was a single bevel of around 23.5 if the promary was 23°. (I'm just throwing out the number 23.5, because I don't know the actual number. What I do know is that the upward force used in the splitting of what is being cut is reduced because of the lower primary bevel.)

Now about razors. Since we have only a fixed primary bevel because of the fixed spine width, we will only be increasing the cutting angle ever so slightly when producing a secondary bevel by adding tape. However if the secondary (microbevel) is shorter in width to the hair being cut, then the hair will be cut at an angle that will "feel" like more than the primary bevel but it will not "feel" like it is cutting a the full angle of the secondary bevel. This is the reason why a secondary microbevel may shave just as well because the angle increase is only a fraction of the small angle increase of the secondary. In other word you will not feel the full increase in angle produced by the secondary bevel.

Problem though is that, as mentioned earlier, the secondary bevel will eventually become a primary bevel. Thus the cutting ability of the secondary bevel will decrease and you will start to feel the full angle of the secondary bevel unless the primary angle is reestablished. Which since we are using tape, over years the primary bevel will slowly creep up in angle in fraction of a fraction in degrees. But we may not see any adverse effects of this in our lifetime.

Like I said, I just wanted to throw my hat in and mention what I have learned on double bevels.