Just recently, I have bought a Sandisk Usb Dual Drive 3.0 OTG (64GB) which is an updated version from the previous USB 2.0. As this is my first purchase of OTG flashdrive, i am quite satisfied with it. It is a plug-and-play device (automatically detected with supported phone). This devices comes with three different capacity - 16GB, 32GB and 64GB with 5 years warranty. This flashdrive uses a sliding mechanism to swith between the USB(PC,tablet) and micro-USB (for phone).
With its tiny design, it has a small lanyard hole which is perfectly suited to be attached to my key chain.
Sandisk Memory Zone Android app which supports the flashdrive has a sleek and clean interface which is easy to apprehend. Not only it provides the user interface (UI) for transferring data between the flashdrive and your internal memory/memory card, it supports other functions too such as private files (EOL soon), automatic backup, upload/download from online cloud services such as dropbox, sugarsync, google drive and monitor the available memory in local momory or external memory efficiently.
I have not run any test on the benchmark yet but found out from this website ,it manage to hit 135Mbps for read and around 40Mbps for write. It is pretty good for its price.
All in all, it's good to have if your phone is out of storage too often. Please be warned that your phone has to be OTG-supported or need to be rooted to support it. Otherwise, do not even consider it. I am using this with my Oneplus One phone without root and it is working fine.