Hello!
We are actively working on the Instance Actors plugin. I think the majority of the work will be going into 5.5 now. So I believe the 5.4 version will not see much more work outside of bugfixes or changes in the .cpp files so they can be a part of hotfixes.
So start using the 5.4 version if you want to investigate the plugin. However, it is still experimental (but we are dedicated to getting it finished) and is subject to having API or header changes that can break code/assets in future major release versions.
-James