Mike, the latest available version of the Curves And Lines Add-in for ArcMap is 4.5, updated about 8 months ago.
The Simplify By Straight Lines and Circular Arcs will convert densified lines into one or more circular arc segments by fitting circular arcs to the straight-line segment sequences. However, the GP Tool will not split the circular arcs out into separate features. If that is the goal then the Split At Vertices gp tool can be run afterwards.
Note also, that the Simplify By Straight Lines And Circular Arcs tool ignores polylines that have parametric geometry segments, IE circular arcs, beziers, elliptical arcs. (It’s in the help under “Usage”)
-Tim