Personally, I wouldn't recommend the Gigabyte H170-Gaming3 for someone who prefers the simplicity of a prebuilt system.
That thing would require the user to read the manual and knowing what could and could not be done with it. When he is expected to know which of the two M2 slot to put that MX300 SATA M2 in and consequentially which SATA port will be rendered ineffective (The D slot closest to the CPU disable SATA3_3, the A slot below the PCIe x16 disable SATA3_0), that's easily one hurdle too many for the guy.
There's also a land mine hidden in the manual (which you can expect a non-techie to throw away fairly soon afterward) that if a PCIe x4 M2 device (i.e Samsung 960Evo / Intel 600p / Plextor M8PeG etc...) is plugged into the D slot, it will knock out SATA3_0, SATA3_1, SATA3_2, SATA3_3, four SATA ports or all the SATA from the two SATA Express ports); it's easily a recipe for a future "How come my MB no longer detect my HDD/SSD" thread.