Of course we can ask the platform if the unit exists already. That's just a more expensive operation and requires more complexity in this code. It's also a less direct way of answering the question "Do I need to write out these files?".

We could assemble a list of the models' ``image_id``s, create a Criteria object based on that, perform a search, and skip this block of code for those units that are found. Or we can call ``os.path.exists`` if we're willing to assume that presence of a directory on disk with the same image ID means I don't need to overwrite it. All this block is doing is writing out those files, so if they already exist, I can skip that step.

For simplicity and efficiency, I went this way. If you think it's better to do the unit search, feel free to make that case.