Sure, get the 1L Tetenal. Just don't mix all the blix up at once; try to mix only enough to process the films you have in a given batch.

If the instructions (and I've never used the Tetenal) allow you an option to mix up the bleach and fix separately, do that. But the chemistry might not allow it; for example some kits have buffering agents in one part that are required for the other part to work properly.