The camera industry is moving toward SD and microSD cards for storing images, but there are still some holdouts, especially at the high end of the market, that use larger CompactFlash (CF) cards. For the ability to read those cards with the latest MacBook and MacBook Pro models, which use only USB-C ports, we tested the Iogear USB-C 3-Slot Card Reader/Writer ($20 MSRP; $16 on Amazon).
The adapter includes three ports to accommodate SD cards, microSD cards, and CF cards, with a single USB-C plug at the end of a short (3-inch) cable for connecting with the laptop. We found it to be a perfectly capable and affordable accessory, with a few quirks.
The primary function of an adapter like this is to transfer image and video files from a memory card to the computer. One of the selling points of Iogear’s accessory is that it supports USB 3.1 Generation 1 SuperSpeed mode, allowing data throughput of up to 5 Gbps, or about 625 MBps.
That’s great, but it’s also overkill: The fastest CompactFlash cards, rated as UDMA (Ultra Direct Memory Access) 7, read data at a maximum of 166 MBps. (A newer specification, CFast 2.0, can achieve up to a theoretical 600 MBps speed, but it’s not interchangeable with CompactFlash cards or readers.)
On the SD and microSD side, the Iogear adapter supports only UHS-I cards, which max out at a theoretical 104 MBps. Faster UHS-II cards include a second row of pins on the back that triple the throughput, but only work with UHS-II adapters that can read both rows.
That said, we found the Iogear’s performance to be solidly in the middle of the pack of other adapters we tested, which included the Cable Matters USB 3.1 Type-C Dual Slot Card Reader and SanDisk Extreme Pro UHS-II USB-C Reader.
To gauge read speeds, we copied 12.9GB of photos (684 JPEG and raw files) from a SanDisk Extreme Pro SD card rated at 95 MBps to a 2016 MacBook Pro in three passes. That resulted in an average time of 2 minutes 47 seconds, or a rate of 77.25 MBps.