Well in this case it's not his fault. I wrote my instructions incorrectly/vaguely, in a hurry at the time. The first line should not read "Extract the RAR file directly onto a CLEAN small microSD formatted in FAT32", rather it's required to do this:
Extract the RAR file to find folder 'SD_Flash_ Kit' and then place the contents of that folder directly onto a CLEAN small microSD formatted in FAT32

I agree with asprin264 that these kits can be dangerous in inexperienced hands but only if they try to make or modify them. Also as Garmin_Nuvi is well-aware, i won't make kits to illegally modify fw (e.g. to use unlocked mapping data), nor will i give ppl advice on how to make flash kits (If they have to ask how, their skill level is almost certainly below requirements). The use of a properly made kit is perfectly safe in unskilled hands as the device will only read the contents of the final folder IF its naming matches the HWID of the actual device. The real danger is in using the wrong Ldr.bin as ramloader in that folder. If an incompatible ramloader is used and so ultimately the bootloader (region 5) has wrong data the device may never turn on again after next boot attempt, i.e. hard-bricked.

Sorry for the confusion mmain, try again. None of this is actually your fault, it's mine. You followed the instructions to the letter but they were lacking, not you.