Without key writing cable you are able to run only unecrypted games. There are plenty, so in that sense you might not need the cable.
I had another issue not having this key writing cable: I was able to select the game, it was written to flash, but then hanged in restarting phase with graphical glitches. Power off the whole PCB -> power ON -> previously loaded game started just fine. Then the same happened with next time I loaded a game. Conclusion is that without key writing cable you have to manually power OFF and ON after the game has been succesfully loaded. I had two A+B boardsets (rev. 6 and 7) with identical behavior. Later I installed key writing cables and that fixed the problem. This problem is not described in the installation manual.
djsheep sells good quality cables in this forum. He has also multi stickers.
I had another issue not having this key writing cable: I was able to select the game, it was written to flash, but then hanged in restarting phase with graphical glitches. Power off the whole PCB -> power ON -> previously loaded game started just fine. Then the same happened with next time I loaded a game. Conclusion is that without key writing cable you have to manually power OFF and ON after the game has been succesfully loaded. I had two A+B boardsets (rev. 6 and 7) with identical behavior. Later I installed key writing cables and that fixed the problem. This problem is not described in the installation manual.
djsheep sells good quality cables in this forum. He has also multi stickers.