As far as I've known and seen there is no advantage except one less sata port, but that's not really an advantage since current boards have been upping the sata ports available
JJ from Asus even says it in one of his videos, that m.2 and even the Asus Raidr are pointless during current times cause you'll get identical or even better speeds just using an ssd or 2 ssds in raid
He did go on to say soon enough tho they be able to make them faster and better in which case they would gain something but some of the recent stuff is mostly just for ppl who want bragging rights lol
CoolerMaster HAF 932 Advanced/ Maximus VI Formula/ I7-4770K/Swiftech H320/ Corsair HX850/ G.Skill Trident X (2x8) 16gb 2400MHz/ 2x 840 EVO 120gb(Raid 0)/ WD 1TB HDD (Backup/Storage)/ EVGA GTX 1gb 560 TI/ Asus 12x bluray combo