Confusion regarding M.2 modules for NUC5i5RYH

Hey there!

So I'm usually pretty good at this stuff, but the M.2 standard is confusing me. Here's my basic question: are all identically notched M.2 SSD's compatible?

I'm considering one of these (probably the samsung):
Amazon.com: Samsung 850 EVO 250 GB M.2 3.5-Inch SSD (MZ-N5E250BW): Computers & Accessories

http://www.amazon.com/Transcend-MTS800-Solid-State-TS256GMTS800/dp/B00KLTPUYG/ref=sr_1_1?ie=UTF8&qid=1426634921&sr=8-1&keywords=M.2+ssd

http://www.amazon.com/Transcend-MTS400-Solid-State-TS256GMTS400/dp/B00KLTPUG4/ref=sr_1_3?ie=UTF8&qid=1426634921&sr=8-3&keywords=M.2+ssd

The spec sheet for the NUC says that it's compatible with "Type M" M.2 cards, but I've been unable to find any M.2 SSD's marked as type M. How can I ID M.2 cards which are compatible besides the "confirmed compatible" list on the nuc spec sheet?

Any help?

Thanks,

Naomi