Seeking advice on the feasibility of a project concept

From what scant details I can gather, this doesn't need to be a regular thing - they expect to pull out a graph every quarter or so.

What about a small SD card in Espruino and write to it (in csv format, for example)? Since it is not an online need, collecting the devices, pull the SD cards an read the data into a spreadsheet (column/row), and create the graph this way?