Any reason I should go M2 and adaptor card over SATA3?

Looking to pick up another SSD to run alongside my current 250GB Samsung 530 but I see that there are options for an M2 adaptor plate to allow the use of a PCI-E slot. Is there any benefit to doing so, or would it be of no real benefit?

I can't see any difference in daily use, slight gain in game loading.

But the Benchmark Tests say it's fast, so it must be

If it's going to be just a data drive. Unless you have money burning a hole in your pocket (or just fancy one) then I would not bother. Just buy another decent SATA based SSD.

PS. What's a Samsung 530? or is it a Samsung 830? or an Intel 530?

Sorry, typo, Samsung 830.

If cost isn't an issue and you cannot add another normal SSD then I would go this route (would install the OS on you M.2 drive as it's quicker than a normal SSD so would mean faster bootup).

If you have room I would just buy another normal SSD though as the M.2 and PCI-E card would be probably the same price as a 1Tb SSD