If, after installation, your system won't recognize the JetDrive SSD as the default boot drive, and shows you an icon same as the one in the pic below, it could be because the MacOS has upgraded its security level for drives. This is more likely to occur in the 10.14 (Mojave) version.
How to solve this:
1. If you have an enclosure for the JetDrive SSD, please place Apple's native SSD in it, and connect the enclosure to your Mac. If you don't have an enclosure, please use an external HDD or SSD with the MacOS installed.
2. Start your Mac, and press the "Option" key.
3. Click on any drive to enter MacOS.
4. Go to System Preferences. Go to "Startup Disk".
5. Select the installed JetDrive SSD as the default boot disk.