We understand your concern: there seems to be an endless list of promising apps that appear to be exactly what you need for your store, only to discover that it possesses a limitation on how large of a store it can accommodate.
Rest assured, this is not the case for Rewind. We have no problem backing up stores of all sizes - in fact, some of our clients run some of the largest Shopify Plus stores on the site! It may take a while to back everything up, but we minimize the time it takes to complete activities through the API.
***As a point of reference, we have found that our backups - on average - can complete approximately 7,000 items per hour. So a store with, say, 23,000 Products being would take approximately three to four hours to backup.***