OK, let me take the Gola (the classic is the 454: 45 keys, 5 reeds on keyboard side, 185 bass buttons with MIII, not convertor).
1) Made since 1956. Golas are still being made but they are no longer the same.
2) The 454 is the classic model.
3) Harry Mooten was a famous dutch accordion player who used a Gola. He recorded Bach as well as light and jazz music. Mie Miki is a younger (and still alive) player on the Gola. Also well known for Baroque music. And my good friend (who unfortunately died almost 2 years ago) Henri Lievens played the Gola. (Thats the Gola I got to repair and tune.)
4) Hohner made them
5) They were made in Germany although I suspect that later more and more parts were made by Excelsior in Italy, who also made the Morino N and S series.
6) The sound and playability of the Gola were second to none, considering the size and weight of the instrument. The Gola was very clearly the top of the line for Hohner. Very fine craftmanship, everything playing very well, right down to the very lowest notes on the MIII keyboard.