Helgoland was the smallest of the German States and issued stamps from 1867 to 1890. A difficult area to collect not only due to the values of the issues but also the many types, official reprints and the occasional forgery.
Above we have from left to right, an original typeII, an 1879 Berlin reprint and an1884 Berlin reprint We also have Hamburg and Leipzig reprints
The Types are mainly distinguishable by the shape of the base of the neck and the end curl of the hair
A Type I - hair end is a large bun
A Type II - hair end is hook shape
A Type III - Hair end is corkscrew shaped
The ever present forgery
A complex country to collect with many challenges. Fortunately there are several excellent books on Heligoland. My favorite is the Kohl handbook that individually describes each stamp