Thanks for your posting. A license is always necessary as a developer if you use SmartInspect to develop and redistribute applications and whether you use the Professional or Redistributable Console doesn't make a difference for this. Only end-users don't need a license if they just use the Redistributable version.
Regarding the comparison: the Professional version has a lot more features and I would recommend taking a look at the SmartInspect trial which comes with a time-limited but fully functional version of the Professional Console.
I hope this helps and please let me know in case you have any further questions.