RPPR uses powerpress. There's a transition feature:
Migrating from PodPress
We made it easy to migrate from PodPress to PowerPress.
Install and enable PowerPress
Configure the "PodPress Episodes" setting in PowerPress to "Include in Posts and Feeds"
Disable PodPress
PowerPress will continue where PodPress left off by including your previously created PodPress episodes in your feeds and web pages.
Sign up for the free analytics service. Other than that, I don't remember any problems switching.