I used the GRII and GRIIIx. When you pick 1:1 in a GR the raw files are crop. There is no return. That makes it really easy to get your mindset right.
I think it was fun, I do documentary photography and it was a real challenge.
I tried 1:1 mode on the GR IIIx given I generally either keep the orignal aspect ratio or go 1:1. My main issue was that sometimes I want the crop to be further towards one edge, given I cannot always control this with candid shots.