I bought a 500 Gb Western Digital Blue M.2 SSD 5 months ago. Put it in a USB-C external enclosure. Best computer purchase I've made this year, at least. Fast, reliable, tiny and portable. I keep my live LR catalog and image files on it. Allows me to move it between my desktop at home and a laptop for the road. I use it on Windows machines, but I imagine it would work just as well formatted for Mac.