I have a mid 2012 MacBook Pro 15", and a mid 2012 MacBook Air 11". Rather than upgrading the internal SSDs, I'm contemplating having an external SSD in an enclosure, where I can boot MacOS Sierra off the external SSD for either the MBP or MBA (not at the same time, of course). Both have 8GB RAM. I'd like to hear the experience of others who have booted a 2012-era MBP or MBA off an external SSD in an USB 3.0 enclosure. I anticipate it will give slower performance compared to an internally-installed SSD, but if the performance off the external SSD is acceptable for daily use (email, browsing websites), then I could accept that. Is that technically feasible -- to boot the same external SSD off two different Macs? I read a recommendation that, rather than using cheap USB 3.0 enclosures, it suggested a Vantec NexStar. So I'd use that.