These OTG devices left us with an overall good impression, even though users may not always get the same results. When attached to a PC as external drives, both the Startech and Thecus devices worked without a hitch. But alas, the data transfer rates we measured temper our enthusiasm. A data transfer rate of 30 MB/s represents the theoretical limit for USB 2.0 performance; only Thecus comes close to this value for read performance, and both devices top out on the write side at 23 MB/s.

The primary intended use for OTG technology - namely, data transfer from a USB-attached memory card or drive to an OTG device - failed to convince us of its real worth. Our decision was not based on the functionality these devices delivered nor the speed at which they worked as both operated flawlessly and to our satisfaction. Rather, we take issue with the half-hearted power delivery systems for both of these OTG devices. They are both under-provisioned and by no means adequate for the requirements associated with this kind of application.

To be sure, the implementation of power delivery to completely mobile storage devices through battery packs is a trade-off between portability, compactness and performance. Nevertheless, a competent design would dictate that there should always be enough power in reserve to keep the disk drive and any attached USB device properly provisioned with power. When users need to start schlepping extra batteries around, instead of more memory cards, we think these OTG devices have missed their design goals by a wide margin.

We’ll conclude with some serious, heartfelt advice about using these OTG devices: Before you take off on an African safari, we’d urge you to determine first exactly how long your batteries will last when backing up data from the mobile devices you plan on bringing along for the trip. Otherwise you risk losing precious memories of that glorious wilderness experience, far from the wall sockets you’d otherwise need to rescue or retrieve your files.