During the first half of the twentieth century, piano accordions became popular in the USA because of their uniformity.   Teachers no longer needed to support many styles of accordions for many European immigrant groups. 

Today, piano accordions are most popular in the English-speaking North American continent, Scotland, Italy, New Zealand, Australia, and some Eastern European countries, while various kinds of button accordions are popular in Scandinavia, France, Belgium and former Soviet countries. 

A piano layout on an accordion provides fast legato playing, and a clear visual relationship to music theory and standard notation.  On the other hand, compared to a button accordion, piano accordions have a smaller range, and difficulty reaching notes far apart (such as two octaves).

Piano accordions frequently go for sale at auction here at low prices.  Check out these deals on vintage piano accordions; new, used and rare.