I think it will be an disadvantage as the other current infantry weapons such as the Ultimax 100 nd the M-16-M203 combo are unable to accept the plastic magazines of the newer SAR-21.
What we can do is to modify the newer Ultimax100 Mk4 variant to be able to accept the plastic magazines and to change the M-16-M203 to the newer SAR-21-M203 combo. This way we can interchange magazines easily during the heat of battle. Comments?