All flashcarts require a MicroSD card, then are unable to use the DSi's card slot. This is because DSi mode hasn't been broken and hence also applies to the DSi Camera etc.
The Acekard requires a firmware update so it can be used on a DSi with firmware 1.4. If your DSi is already updated to firmware 1.4, you will have to perfrom the update on a DS Lite/ DS Phat or DSi with Firmware 1.3.
ShopTemp will preupdate them for you if you select that as an option when you add it to the cart. See
Premium Update + Flashing Service.
I have a guide in my signature if you want to know more.