Hi, as I wrote to all customer (via direct email) you should wait still a bit of time before move from newsletter pro to free with modules, since the modules are tested but migration is not still stable.
So, right now, you should keep the pro version. I’m already writing the migration path but since some themes of feed by mail must be recoded, the module is not fully ready (or it is ready if you want to reconfigure it and use a different theme).
Stefano.