Well, that thread is really vital. Concerning your implementation: Have you documented it somewhere?

BTW: Have you considered transmitting the "generator" field as well? See: https://www.w3.org/TR/activitystreams-vocabulary/#dfn-generator

In Friendica we use this field. It could possibly help with different group implementations to detect how this has to be handled by the other side.

If you need to implement special behaviour based on software name it's a sign something has gone wrong with the protocol

I can think of a couple special behaviors implemented based on software name in #Friendica, but to be fair we are trying to be compatible with several different platforms.