I would say that the SafeSiders improve instrument efficiency by about 25 percent. The increased taper encourages better irrigation with 5.25 percent NaOCl. The flat creates an open space for debris. While the flutes on one side are relieved, the central core of the instrument is not, leaving the instrument essentially as strong as it was before. Yet the rotational force needed to negotiate apically is significantly reduced, allowing total instrumentation with a light touch.
Less engagement means less resistance.
The small reduction in cutting ability is compensated by rotating the instrument an extra turn, something the dentist does automatically anyway. The net result is that the instruments glide through the tooth, reaching the apex quickly and efficiently. The first eight instruments are tough stainless steel, and the last two instruments in the sequence are nickel-titanium. They are used to size the canal to accommodate the tapered gutta-percha point that is to be placed. They are never rotated beyond resistance.