CBA or Chromatic Button accordeons are also known as Continental Chromatics.
They come in "B" systems or "C" systems. also known as B Griff or C Griff.
They are usually 4 row or 5 row.. I have seen 6 rows but these were the Russian versions known as BAYAN.

These are not diatonic.

If I were starting accordeon all over..I would start,and stay with a CBA.