Firstly I would like to thank again for the writeup, it was one of the best guides to get started with Mcuboot.

I noticed a minor misinformation though. The --pad flag is not actually needed when preparing the primary application. It works fine without the option, furthermore it reduces the image size, which in turn reduces the amount of sectors to be copied when swapping.

Also in the imgtool docs it says:

The optional --pad argument will place a trailer on the image that indicates that the image should be considered an upgrade. Writing this image in the secondary slot will then cause the bootloader to upgrade to it.

It does not seem to be a prerequisite for the primary image. What was the reason you added this option?