I checked some resources, TA-t3 is right about the flash card features. Operating system can support wear levelling, also SD controller supports it as well. But not all SD card support that, many cheap ones don't. As for MM2.x writing to flash card, I checked the source code, it does write that many times. Since for every tile downloading, the code does a "sync", that's the flushing the file to the disk. It will write to header, hash table and data section.

syzygy, I guess your hardware key problem is due to that you use MM2.x before, and its key configuration method/value may be different from the MM1.x, and downgrade may confuse the MM1.x. BTW, I didn't change anything in both MM1.x and MM2.x except replacing their file system, so the problem may well be from the incompatibility of the two. I need to look into the source code to see how old MM1.4 and new MM2.2 handle the hardware key and replacing tile issue, to find some resolution for you.

BTW, since this is the engineering experiment to probe the way to improve MM, so I tried to limit the code change as small as possible.