I have an SSD USB 3.0 drive that has my Lightroom library. It plugs into my iMac at home (via the fantasticElgato Thunderbolt 2 dock), but on the road, I like to use it with my 2011 MBP to access the same Lightroom library. The problem is that it is a LOT slower since it can't take advantage of the USB 3 speeds. They do make SSD drives that connect over thunderbolt, but they are much more expensive than the USB 3 counterparts. If you plan to only use one drive, the price differential (around $60 for a ~256k drive) might not cover the price of the StarTech.com Thunderbolt to Gigabit Ethernet with USB 3.0 Adapter (~$80), but when you consider being able to use USB 3 thumb drives or other USB 3 drives you might want to use on occasion, the difference in price for the extra speed from many more peripherals starts to add up.
The Startech came along right as I was considering the new MBP. The new MBP only has USB-C ports, so a product like this, combined with a thunderbolt to USB-C adapter (which I need to attach it to the Elgato dock anyway) will add ethernet and USB 3.0 to one USB-C port. I plan to test this when I get my hands on the new MBP. That capability combined with what it offers to my 2011 MBP makes it worth the price. I could use it at home with my 2011 MBP, then when I go on the road, detach it and use it with the new MBP where the extra USB 3 port and ethernet will come in handy.
For my current purposes, I plugged my USB 3.0 SSD into the USB 2.0 port on a 2011 MBP. The speed test showed a read and write speed of 30.3 and 34.8 MB/s. So slow, but it is what I deal with because I didn't want to buy SSD thunderbolt drives because they cost so much more. I then unplugged the SSD, plugged in the StarTech device and the speeds increased 10x! (353.2 & 355.6, respectively). Once again, the saving grace to these 2011 Macs is the often criticized thunderbolt port.
The Wrap Up
One thing I should mention is that this was plug and play with my 2011 Mac. I simply plugged it into the thunderbolt port, connected it to ethernet and to the USB 3.0 drive and everything was up and running in seconds. Also, the size and weight of this thing makes it easy to toss in the bag with my SSD drive.
If you are in a similar situation, where you are stuck wth USB 2 ports, but have a thunderbolt port, I highly recommend this device. If you are looking at new Macs and the required dongles, it may be cheaper to get a USB-C only device, but I like the flexibility of using it with my current Mac and my future Macs.