I have OWC 480Gb SSD for MacBookAir mid 2012. I called OWC to ask the same question. I was told that it actually was a Heat matter, that it would work but at my own risk. I feel I was lucky to get that response and that they probably do not give it any more. I tried it with success, keeping the Enclosure lid open. I would not use it extensively though. For extra safety you can always use a small fan to cool it up. I think you can respect their recommandations by booting from the external enclosure with the original Mac SSD in it and then Clone it to the internal freshly formatted OWC SSD. I now have another OWC 480Gb SSD for MacBookAir 2015. Am I going to have the guts to also give it a try ? Just to play safe I will try not to. So I would suggest that a Heat Monitoring Program be installed and that both Original Apple and OWC SSD Temperature be monitored and compared.