Hi Jan-Filip,
Congratulations, you found a hidden feature that even I didn’t know about! 
Joke aside, sdkperf as a receiver isn’t really meant to be used to try to parse messages. The most you get with regards to functionality for displaying messages is a raw dump via the ´-md´ flag (message dump). I was told by one of our engineers that the flag you found was added for some internal debuggin purposes (related to distributed tracing) and that it isn’t meant to be used to parse messages on the receiver side.
So if you are using it and found a way to parse messages in creative ways - well done, but -, please be aware that it’s an undocumented ´internal´ feature and don’t rely on it staying unchanged (or included) in future versions. 
Best regards,
Christian