A question on balun

I want to buy some baluns but I am not familiar with the balun based on transmission line. I am not certain whether it is bidirectional,i.e. can it be used as unbalanced-2-balanced as well as balanced-2-unbalanced transformers. Thanks for any help

Baluns are basically passive impedance transformers.
So they can work bi-directional.
If the manufacturer says that it needs bias then those might not be b-directional.