I recommend you getting a Acekard 2i, why cause basically there´s almost not anymore updates from the M3 Team Also, Acekard 2i is an better flash cart which gets constant updates from the AKAIO team, and on top of that it works with 1.4 update, so go here:
Acekard 2i from Shoptemp this is GBATemp official shop website in which you will get an excellent customer service. Believe me you will not be dissapointed with
Shoptemp.You may also want to try the
SuperCard DSTWO from Shoptemp the new flashcart which includes: Almost perfect DS Roms Compability, RTS(so you can save the game whenever you want and then continue it there), In Game Guide(to be able to open walkthroughs, game guides and more), In Game Cheat(be able to use cheats while on game, Stylish GUI, and an antipiracy patch database, a GameBoy Advance Emulator.Also in future releases(which the team Promised): DivX/Xvid movie playback(which will accept many formats like .avi,.divx,.xvid, and many more instead of the troublesome .DPG video format which most flashcards just accept), Snes Emulation, and many more. And it also comes preflashed for 1.4. You may also want to check GBATemp's
SuperCard DSTWO Review
ANSWERS
That M3 Power Cable its for updating its Bootstrap so that it works with DSi Firmware 1.4, however Acekard 2i doesnt has it cause it is not necessary.
Yes, for the M3 you need to put the files on the micro sd and it will update itself.However, on the acekard you need an DSi pre- 1.4 firmware and put the files on the Micro SD and open them and it will update.
BTW, if you meant updating the software(GUI,OS,Firware) of AKAIO or M3 Sakura, you just download the lastest updates and replace the old ones.
PS: If buying an Acekard 2i put the AKAIO firmware, find it on GBATemp.net on the downloads Section, AKAIO is the best firmware avaible for the Acekard 2i.
Also, when your Acekard arrives(if you order it) follow this guide:
Acekard 2i Setup Guide made by tk_saturn to set up your acekard with the latest firmwares and update it so that it works with 1.4 update.
If you do not have an friend DS, DS lite or a DSi (on 1.3 firmware) a friend with one you may want to order in shoptemp a micro SD Card and Premium Update+Flashing Service so that it is ready to play outta the box.