FYI Jon, I know you already made your decision but in the name of full disclosure, I have more to add to the thread.
After your thread and three or four emails from OWC, I decided that even if the Envoy Pro mini enclosure was too big to fit comfortably in the USB slots on many — maybe most — Macs, it looked too useful to ignore and it arrived this afternoon. V1 was correct in his caution that it might be too wide and too fat to fit comfortably into the USB 3 slot on a lot of different models. However, although I cannot find it listed anywhere in OWC's description, included in the box with the
Envoy Pro Mini Ultra-portable SSD is a handy-dandy twelve inch USB pig tail that will fit virtually any USB port comfortably. It works great on my 2012 Mac mini.
Benchmark speed tests on the Envoy show an average read speed of 431.266 MB/Sec and write 374.715 MB/Sec. Compare that to a 5400 RPM HD on the same USB 3 bus at read 174.166 MB/Sec and write 171.864 MB/Sec. I think it is going to serve me well as an emergency drive.