"My Mac Mini does not recognize the new second drive Transcend 820 SSD"に関する回答JetFlash is preformatted with MBR. So use Disk Utility to erase and format the device with GPT (GUID Partition Table). Carbon Copy Cloner works great for cloning. Also fixes the recovery partition. Or can clone for free with unix tools. BlackMagic Disk Speed Test says write up to 620MB/sec; write about 720MB/sec.
"My Mac Mini does not recognize the new second drive Transcend 820 SSD"に関する回答Transcend website says macOS High Sierra 10.13 is required. My Mac Mini late 2014 running Yosemite 10.10 recognizes the drive as Apple 128 GB SSD and can be formatted at that capacity.