Great app and the simplest way to test your external SSD/Flash drive
For those who wish to use the iPhone 15 Pro Max for writing to external storage, particularly when recording in the highest quality format—60 frames per second in 4K with Apple ProRes—you must use this application. It's the only method to determine if your external SSD is sufficiently capable. Additionally, ensure that your external SSD is formatted in the Apple File System (APFS) format, with a GUID Partition Map as your partition scheme. Failing to do so could result in dropped frames in your footage, which can be extremely frustrating. Also, make sure you choose the right format for testing: ProRes 422 HQ in 4K.