Let's not talk about whether 1-bay is enough or not. There are users particularly like its simplicity.
WD mycloud 1-bay NAS is an all-in-one device of which the HDD is not user serviceable/replaceable. As per its design, when the HDD dies, the NAS follows (talking about after warranty period). In contrast, S/Q 1-bay NAS can use any HDD brand/model as long as it's within the compatibility list. I would choose the later for the sake of flexibility and continuity.