Vertolot,
I've used the 2101+ fairly extensively. As others have said, it's not the least bit intuitive. However, it is a fairly capable unit. If you'll be going back and forth between it and another nav system you have my condolences. But, if you'll be using it exclusively, with a few months practice I think you'll find yourself very comfortable with it in all conditions and won't even notice the poorly designed user interface.
Several years ago Trimble distributed a tutorial for the model 2000, which is very similar in operation to the 2101+. They included a rather nice interactive trainer which operates fairly well on older computers. However, I've seen it experience problems on some newer ones.
If you'd like to PM me perhaps we can attempt to figure out a way to get a copy to you.
-Stan-