RSX as is is most usually defined as "smoother RSI", and it is correct in most of the cases.
uses in its calculation what we could call a momentum using period 1.
This version is a variation and allows you to use instead any momentum
length. Of course, it carries added lag with it (when the momentum period
is increased) but in some cases (if the momentum period is increased
moderately) it can filter out some false signals.