We designed these with two functions in mind.
The first and most obvious role was to act as a coupler to join two mags together, allowing for an extra 5 rounds and the extra purchase the doubled up mags provide.
The second purpose was that the coupler be used with a single magazine as an alternative base plate. It adds that critical extra length to the mag (easier to insert and extract) in the case of a 5 round mag and is far easier to deal with than the original baseplate when it comes to removal and replacement for maintenance purposes.