I have a P30+ and AFD-II with mask.
I seem to recall two rectangles within the view finder.
Generally, I'm not shooting that fast, lets say max 10-15 frames in a pose, and 3-4 minutes to shoot it, at that kind of rate, the frame lines have never been an issue. This is in studio/strobe setting.
Painting with a very broad brush, given that I work with all levels of models, I really never have problems with them either moving out of the single point focus comfort zone, or with the crop. I will add that all my work is fine art figure, so once I get the model in the light I want, moving them 1/2 and inch here and there is what I really need from them.
If I were shooting fashion glamour, flamaour glashion or what ever the term is these days, my setup might not work so well .....
I did just shoot swim team portraits for my kids team, and looking at the results from a D300 I wonder why I even bothered ..... Should have done the whole thing with the P30+ it would have been more than up to the focus/speed/framing needs. The team shot would have been great for the 35mm lens .... I have a feeling that given nothing bigger than an 8X10 is needed, and most if not all parents have at best and AFC canikon with a kit lens that IQ of the D300 24-70 2.8 will be fine, but it bothers ME looking at mush in post.
Dave