These tools allow you to quickly check if your metadata 'looks' correct... are there the correct number of image blocks (i.e. one per tile if multi-scan image)? Are the dimensions correct? etc.
''What if I cannot read my metadata via a GUI?! '' =
Did you observe a problem with your metadata via a GUI? Was there no data at all? Or was metadata missing? If this is the case, then perhaps there are structural issues with your metadata that require a bit more in-depth inspection via command line tools.