When looking to attach a file, I can choose to select from the computer or any of the attached cloud storage services.
You also provide the option to use any of the files that may have already been uploaded for that record.
What you do not provide is the ability to access the repository of all the files that have been uploaded for that product.
This becomes especially important when considering your MOCKUP functionality.
For example, I create a feature, we brainstorm and we use the mockup to outline the high level point. The mockup is saved, attached to the feature and is available to view in the files section.
To reuse the mockup or any other file that has been uploaded and visible in the file repository, I have to download the file, and then re-upload it again using "select from computer".
This is an awful customer journey experience. You should allow for a new repository category to appear called "products files" or similar and be able to reuse files already uploaded that way.
I have attempted, rather crudely, to show you what I mean in the attached files.
By doing above, you sole the mockup and the files in one go. I have been training over 150 people in using Aha recently and this is a common issue in the feedback.