The futur is quite a bit larger, it is supposedly very aggressive. The blade gap is huge, at minimum more than the progress at 5.
I quite like to feel the blade & don't go above 4 on my progress, so a futur is for the brave.
Fatboy isnt that fat really, for the 50s it may have seemed so. Paul H on YouTube has both and you can see how different they are in use. I think Rockwell are coming out with a tto adjustable this year, that might be a closer modern alternative.
I recommend putting your name down for the Fatboy pass-around, see how you go.
If you like it, only a Gillette adjustable shaves like it. If you don't it sorts that out just for the cost of post.