No mate, nothing like that boots super fast. It must be the adapter. I'm on Mojave though so still 156 boot room. Only thing I've noticed is my Macbook sometimes turn itself on. Happens twice but not sure if that's related to SSD.I also have Retina Mid 2014 13'' and instaled Intel 660p nvme ssd 1TB to a sintech long adapter, but I'm always getting drive showing as external (yellow icon) at boot so I have to wait 30 seconds to boot from drive. Do you have that kind of problems or not? Sleep, hibernate works like it should.
I am using Catalina beta 8 with bootrom 157.
P.s. Drive in system report shows as internal. Is this maybe adapter fault, I already tried two of them. I also tried on Macbook Air 2017 and it works without problems.
Drive shows like that: