Lenovo T430 M2 Slot

OK, before I buy one of these, I want to be sure I know what I'm getting into. I looked at the user manual] and found several notes about the M.2/NGFF drive slots. It has two, in addition to a 2.5' drive bay. But... when I read the manual, it says:

Lenovo T430 M2 Slot Reset


Thinkpad T430 M.2 Slot

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Learn how to use the PC Card/ExpressCard reader on your 3000 Family or ThinkPad notebook. A SIM card slot is safely hidden behind the battery compartment if needed, so users under major cell phone carriers in the U.S. Should feel right at home with the T430s. Because of the location of. There is a memory slot accessible on the bottom of the machine where I can add a single 8 GB SoDIMM. I don't see any second slot nor is there anything indicating where that would be. The product page says I can upgrade the laptop to 16 GB, it currently has 4 GB. Overview - ThinkPad T430, T430i, features and specifications for ThinkPad T430, T430i. Detailed Specifications T430, T430i- Architecture - Communications- Expansion - Power- Operating Environment - Security- Software - Storage- Video Lenovo Inc.

• If your computer is equipped with both a hard disk drive and an M.2 solid-state drive, do not use the
M.2 solid-state drive as a bootable device. The M.2 solid-state drive is used for “cache” function and to
support the Intel Rapid Start Technology.
and
T430
• If your computer is equipped with both a hard disk drive and an M.2 solid-state drive, you are not
recommended to use the M.2 solid-state drive as a bootable device. The M.2 solid-state drive is designed
and developed for the “cache” function purpose only. If you use the M.2 solid-state drive as a bootable
device, its reliability is not guaranteed.
User Manual Link

Lenovo T430 M2 Slot Drivers


My question is... why all of these caveats? Is there some sort of technical reason I couldn't or shouldn't use an M.2 drive as a bootable drive? Why have an extra slot then? Why would it be 'unreliable'?

Lenovo T430s M.2 Ssd


Lenovo T430 M2 Slot Car

Could someone with some expertise about this sort of drive and/or Lenovo weigh in here? I understand that NGFF drives are new, expensive and at this point are often used for caching, but I'd guess that over time capacities will expand, and it would be nice to be able to upgrade down the road and move my boot/system drive over to a new SSD. But I'm not going to buy something that I can't upgrade.