I read on one of the forums that these APIMs should not be upgraded to version 3.4 because they get damaged. But no one wanted to explain why this should not be done. But since you write that these APIMs can be upgraded to version 3.4, I will update them. Reformat is always done at your own risk.
GJ5T-14G371-CFC is an “ancient” APIM, there’s always a risk while reformatting an old APIM…
But again, it should not be bricked if the APIM is healthy…