Dev cartridges for DS and GBA

I recently received a couple development cartridges (not the whole kit), and was wondering what their utility was, as well as their value. The GBA cartridge has the codes E201785 and E201629, while the DS has E202395, E202510, and "Nintendo M10-X1." Both have a 64K EEPROM attached. How can you write to them? Would it be worthwhile to sell them, or would I be better off keeping them?
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