What do you plan to use this drive for?
In the M.2 port, it will run much slower than its rated speed.
In an adapter in a PCIe slot, it will run at its full speed, but you may not be able to use it as a boot drive.
Indeed, with Intel's 660P in 1 TB being at firesale prices, I'd sure live with it costing less that standard 2.5" SATA, and being 'only' ~100% faster in sequential reads. (Alas, this will only translate to 1/4 sec faster boot times)