Any practice is worthwhile, but be aware that mistakes can still be made - from both native and non-native English speakers.

Of course it's useful, but bear in mind that although you are having practice, both of you non native English speakers could be making a lot of mistakes.

A lot depends on what your level is. If you are not very fluent, it may actually be easier to build up confidence when talking to a non-native speaker. It's more about how much patience the other person has. If you are quite fluent, you will benefit more from conversing with a native speaker, of course. But.... I'd say it's all good if the person is fun to talk to ;-)

Why not? We can help one each other.

yes,don't you think so?