As of version 0.1.0 of All of Fabric 6, version 1.5.3 of the "MEGA Cells" mod is in the pack.
However, that version has a bug where dismantling a MEGA storage cell voids the component inside, leaving only the housing. This can result in loss of thousands of gold and certus quartz as a new component needs to be crafted to rebuild the cell.

Dismantling ME Storage Cells with a capacity of 256 kB and lower works properly, returning the proper Storage Component along with the housing.

A workaround is to update to a beta version of the mod as all beta versions after 1.5.3 have a fix for the bug.

Originally found in All of Fabric 6 1.5.0, but the mod has not been updated since its original inclusion in 0.1.0.

Confirmed fixed. MEGA Cells 2.0.0 has been released which adds new features and fixes various bugs including the original bug reported in this issue. The new mod version is in the latest modpack release (1.8.0).