When you add your students to your list, they're not required or invited to sign up to Ubindi.

Your students can see your class schedule on your Ubindi page.

You can send your students messages through Ubindi and, since these go directly to their email inbox, they don't need to sign up to read them, or respond to them. 

Similarly, you can take class attendance without anyone needing to sign up.

There are however a few cases when your students will need to sign up, because you will want to know who they are if they do any of the following: