Questions about Transcend JetDrive 825

This is an SSD upgrade kit for a Macbook Pro/Air. The idea behind it is that you remove the SSD from the MacBook and insert the larger one of the kit. The case is then just so you can still use the old SSD as an external hard drive.

I have a Transcend JetDrive 825 (960) like this. Mine definitely has a TB1 or TB2 connection! Nothing with TB3. In terms of speed, the drive achieves about 600 MB/s write and about 740 MB/s read, which would be more like a TB1 10Gb/s. I'm not sure if the TB interface is the bottleneck. Not sure if the TB interface is the bottleneck though. Internally, the same SSD achieves over 1,400 MB/s, so it is at least to be assumed.