Limits

Fifty files, a hundred megabytes each

Those are the ceilings. The practical limit is usually your patience, not the tool.

A task takes up to fifty files. That is generous enough for a year of receipts or a chapter-per-file manuscript, and it is the same ceiling whether you are paying or not — the subscription changes what you can download, not what you can process.

Large merges

Fifty scanned pages at full camera resolution make a document nobody can e-mail. If the result will be sent rather than archived, consider merging the photographs separately and keeping the text pages in their own file.

Mixed sources

Pages from different sources arrive at different sizes — A4 next to US Letter next to a phone screenshot. They merge without complaint, but the result will have pages of varying dimensions, which is fine on screen and visible in print.