There is a reason the SI system uses decades. It's exactly that it makes this trivial, but I guess if one is not that accustomed to thinking in decimals/metric, it might not be as obvious.
mg is also just composed of the SI prefix m = milli, and the SI unit g = gram, where the latter is a little weird due to naming problems early on leading to it being the only SI unit where the base unit, the kg = kilogram already has a prefix.
The milli means thousands, so you are just saying 6 thousand thousands gram. If you internalize SI units, and decompose them automatically, this seems at least confusing, possibly worse, depending on how picky the reader is about unnecessarily contorted grammar in general.
I myself advocate the use of prefixed gram for the cases where people use tons, but I accept that people in general don't like them being called megagrams = Mg from now on. This is by the way the reason why mb != MB when denoting storage space, but 8e9 mb = 1 MB, due to the former denoting millibits, and the latter megabytes. There is also MiB, mibibytes, denoting 2^30 B. Microsoft denotes MiB as MB, which is wrong, and lead to great confusion. Be careful, embrace SI units, they make your life easier.
Using SI doesn't mean you shouldn't maintain consistency between units you're actively comparing to avoid inadvertent conversion error. If your working units are mg, using mg across the board is completely sensible. It lowers the mental load involved and reduces the chance of the human factor introducing errors.
It has nothing to do with being uncomfortable with working with SI units and everything to do with having a consistent working environment for me.
For example, If I were drawing something up in CAD and needed a particular face to be 120mm, I'm completely aware that could be represented as 12cm, but I want the software to label that as 120mm so that it's consistent with e.g., a 23mm face next to it.
Your working units for sodium in food consumption are milligrams. Labeling the final sum the same way is a good thing.
That'd be ideal, yes, but I'll take 6k mg over 6g when mg are the working units every time. The k makes it much more explicit that there was a shift in magnitude than just silently converting between units.
It might look wrong in isolation, however the choice of unit do add context to a conversation. For example, there are instances where one would say "twenty hundred" instead of "two thousand". Sodium too is typically denoted in milligrams because most other micronutrients are measured in the same unit.
mg is also just composed of the SI prefix m = milli, and the SI unit g = gram, where the latter is a little weird due to naming problems early on leading to it being the only SI unit where the base unit, the kg = kilogram already has a prefix.
The milli means thousands, so you are just saying 6 thousand thousands gram. If you internalize SI units, and decompose them automatically, this seems at least confusing, possibly worse, depending on how picky the reader is about unnecessarily contorted grammar in general.
I myself advocate the use of prefixed gram for the cases where people use tons, but I accept that people in general don't like them being called megagrams = Mg from now on. This is by the way the reason why mb != MB when denoting storage space, but 8e9 mb = 1 MB, due to the former denoting millibits, and the latter megabytes. There is also MiB, mibibytes, denoting 2^30 B. Microsoft denotes MiB as MB, which is wrong, and lead to great confusion. Be careful, embrace SI units, they make your life easier.