Byron,
We started a Mijoshop plugin, but stopped development of it after they were removed from the JED. There's no judgement on our part about the quality of the extension, but not being on the JED has led to a direct reduction in the requests for Mijoshop integration.
As for JFBConnect itself, we create 100% standard Joomla users. When you say "otherwise it is kind of useless too me because customers will need to login twice", I'm not sure what you mean. When a user registers/logs in with JFBConnect, they should be recognized by Mijoshop (or any other extension) without issue. They shouldn't need to log in again to Mijoshop that I'm aware of.
The only thing our Social Profile plugins does is allow for the importing of profile data into 3rd party extensions. If you're looking to add social network login buttons to any pages of Mijoshop, you can add the following tag to any of the Mijoshop template files:
I hope that helps explain, but if you need anything else, just let me know.
Thanks,
Alex