testing 11.2.0.3 > 12.2.0.1 with datapump, use transportable tablespaces or not?

Both databases on Windows Server, going from 2008 > 2016 versions.

I'm preparing to do some testing on upgrading, the source database is live and can't be put in read only at this point, and a consistent export isn't important for initial testing purposes.

I've done a conventional DP export with Version=12 set, and ready to import into new server, new shell database has been created with needed production tablespaces also created

Since I've never done a transportable tablespace export-import, I am thinking about trying one, but from what I've been reading the source should be in read only mode, but I don't know if that's mandatory or just recommended for consistency.