In their 1925 catalog Barnhart Bros. & Spindler caution against overuse of the extenders:
These characters impart a most pleasing touch of decoration, but as a general rule not more than one should be used in any line, with exception of ll in a top line.
And a note on the alternate caps: the M and N have both a rounded and a pointed version. Although contrary to our present tastes, the rounded letterforms are the standard, and the pointed ones are the alternates. This is borne out by the rounded form of the caps U and Y which have no alternates.