Right off the bat one of the major security concerns with Apple is that whenever you send it for service, you are surrendering custody of your SSD and Data. Obviously, since the drives are soldered in, they don't have the ability to offer an option such as Lenovo's Keep Your Drive service.
If you don't have anything sensitive on your drive, it isn't a big deal. But if you do and the machine fails to power on giving you the ability to wipe the drive prior to service, your sending that data in and hoping it the data remains secure when you do. Do you trust Apple and everyone who works there? You will have to in that case.
In no means can the data on the SSD's be passed to a 3rd party such as Apple, as it effectively becomes uncontrolled once in their hands.