There are many plug in boards for the Raspberry Pi model B (2 x 13 pin connector) which are now not compatible with the Model B+ as this has 2 x 20 pin connector. Even if they plug in, they can interfere with some of the components as the position of the GPIO has moved.
Fortunately the entire Custard Pi range is compatible with the Model A, B and the Model B+.
Fortunately the entire Custard Pi range is compatible with the Model A, B and the Model B+.