For EIS, there is not too many problems. They question is on how to convert the potential. In the device, you don't have the reference from what I understanded, that means you can not compare your data from different experiments directly, even the same experiment but different times. Of course, you can use them in paper, but must mention how you get them.

A sandwich configuration is acceptable if it is carefully implemented, thoroughly characterized, and properly documented. You must demonstrate that the method does not introduce significant artifacts and that the results are reliable and reproducible. Always provide a clear explanation and justification for your methodology.