There's no "normal" M.2.
It's mechanical/physical slot specification and doesn't have any "basic mode" everything is supposed to work at.
NVMe protocol using PCIe SSDs and SATA SSDs are just one of the different applications for it.
That's how Crucial MX500 and WD Blue 3D, which are SATA SSDs, can be available in both normal 2.5" SATA drive form factor and as M.2 card.
As for gaming use there's little if any real world loading time differences between NVMe and SATA SSDs, regardless of what kind synthetic benchmarketing numbers marketing touts:
https://www.youtube.com/results?search_query=nvme+ssd+hdd
So choise should be primarily made on based to can you afford extra cost for little benefit and for price per GB.
And even if wanting advantages of NVMe protocol and faster than SATA speed for some occasional file copying, there's no sense to pay some Samsung prices.
Corsair MP510 is lot cheaper with reasonable price extra over SATA SSDs and doesn't even lose that much in synthetic loads.
For budget Corsair's older gen MP300 could be actually found for same price as SATA SSDs.
