The underlying ETA API has a maxFragmentSize setting. It is the maximum size buffer that will be written to the network. If a larger buffer is required, the RSSL Transport will internally fragment the larger buffer into smaller maxFragmentSize buffers.
For RSSL, the default maxFragmentSize is 6144 bytes.
MRN also uses RSSL protocol so the size of buffer that is written to the network will not exceed 6144 bytes.
I believe that they cannot be directly compared.
With MRN_STORY, you get both Headline and Story body. But with N2_UBMS, you get only the headline and you must send additional item requests for the Story body.
But MRN should utilize fewer network resources if you need the Story body of every news. This is because: