major bug for me, my raw files from canon 5d mark iv wont let me quick view preview, its just black, I thought my photos were corrupted but its only quick view
Ok, I did. And even the Full Installer 15.4 (24E248) still borks the Firmware if you switch from or to 15.3.2.
It seems ok if both drives have 15.4 on them. I am currently running a 256Gb model from an external 1TB drive.
It does mean that once you have upgraded to 15.4, any drive you boot from (internal or external) has to be 15.4.