Choosing the toilet underneath
These are WASHLET+ sets, so the toilet is designed around the seat and the cord and water line stay hidden behind the skirt.
Nexus and Drake are the most popular bases. Aquia IV adds dual flush. Check the rough-in on the model you want — most are 12 inch, and the alternatives vary by series.
What the S7A adds
The S7A is the S7 with auto flush and a slimmer profile. Both share the features that matter most: water heated on demand rather than stored, so it never runs cold mid-wash, and EWATER+ misting to keep the bowl and wand clean between uses.
S7A or S7?
If auto flush matters to you, the S7A. If not, the S7 does everything else for less. The wash itself is identical.