X250 with M.2 and dual OS

[Koulou]

Hello guys

I recently bought a second hand X250 with an Intel 240gb SSD installed and I am planning to install also an M.2 SSD to install Linux.
I have already installed Linux in another partition in the Intel, but in general I am not a big fan of grub and also I don't like the restriction of maximum 4 primary partitions per disk. I would prefer to keep the Windows drive 100% clean of any Linux staff.
So, I'm planning to install my Linux in the M.2 drive (I have already cleaned my system disk of the Linux staff, grub etc) and I was wondering if choosing the boot up device from the bios is going to be an option, without grub or other boot loaders. I just want to leave the Intel as default boot device and when I want to boot up in Linux, I will choose to boot from the M.2 SSD.
Will such a setup work in my Thinkpad?
As far as the M.2 drive itself, a 120 gb is more than enough and I am planning to go for an ADATA. I have read a lot of negative reviews about the Transcend M.2s and I don't trust "random" manufacturers, like ZTC or KingDian. Is there any better option for me?

Thank you very much for your time. I 'm looking forward to your replies. Cheers

[hengster]

After you install physically the m.2 ssd and virtually the Linux on it, restart the ThinkPad and press F1 at boot to get into Bios.
Set the boot order of the 2.5" drive with Windows as higher priority than the m.2 with Linux, so Windows would be default OS.
When you would like to boot to Linux, press F12 during the boot screen to select the boot device.
As for makers, m.2 from Crucial, Samsung or HyperX (Kingston) work just fine, though you may not find 120gb but only 240/250/256gb ones.
The X250 only accepts 42mm length shortest type of m.2, so get the 2242 versions, not the 2260 (60mm) or 2280 (80mm).