That tag looks to be the proper tag. If it's not rendering, please check the following:
* You have the JFBCSystem plugin enabled
* Try disabling all caching in the Joomla - Global Configuration area as well as the System - Cache plugin (if enabled)
* Check if you've configured an "Admin Render Key" in the JFBConnect -> Social -> Misc configuration area. If so, you need to use that key in the tag. So, if you're key is '12345', you need to use the following tag:
{JFBCLogin text=Or, login with key=12345}I hope that helps narrow down the issue, but if not, just let us know.
Thanks,
Alex