It's about 5 times as thick as a credit card, but otherwise matches the remaining two dimensions. It has storage-only slots to hold 2 microSD cards very securely, one M2 card (untested), and one SIM card (tested, holds well). In a pinch, a microSD card can be slotted into the SIM card slot and will hold fairly well, but not as well as the intended slots. There is one reader slot that accepts M2 or microSD, and while it's not the nice spring-eject type, it does hold the card securely and could also be used to store an SD card. The male, full-size USB interface comes out of the card with a slide-button that locks in the extended and retracted positions (press in to unlock), but it's just the piece with the contacts and so fits entirely into the mated port. A small green LED lights when the unit is plugged in, and blinks while reading or writing. I read and wrote via the reader several times, no problems--didn't benchmark the card via it, though. It's all plastic, and feels neither incredibly durable nor flimsy--it should last a while with care. Overall, I'm a fan. :-)