I'm not sure how he thinks this will work on an iPhone 6
With the iPhone 5 and earlier the AES key and try count are stored on the flash chip. Reloading that chip with a copy will reset the count of tries. On the iPhone 5S and higher (anything with an A7 or newer) the key information and count are stored on a secure area of the CPU chip. Taking an image of the flash memory will have no effect on retry counts or prevent the key from being erased.