I tried it to create an atlas with output from the plugin and had problems, but got it to work, eventually! (disclosure - I'm the plugin author)
The plugin creates a memory layer. It seems that you can't use memory layers as coverage in Atlas. But you can get around that by saving the layer as a shapefile or other format (I suggest you do this anyway, as the memory layer will be lost when you close QGIS).
To get around this,
- set the CRS in the memory layer if required (the plugin doesn't do that at the moment)
- save the memory layer to a new shapefile layer
- use the new shapefile layer as coverage in the atlas
- add a piece of text, and use the following expression
This is map [% "name" %]
Name is the field which contains the cell reference (A1,A2,B15 etc)
You should now be able to produce one map per grid square, like this...
.. or with an overview