If you look at an older-style internal BB, you'll notice a gap between the butt of the crank arms & the frame. External BBs fill this gap, so the overall width is basically the same. The downside is that you can't adjust the "Q-Factor" - the lateral distance between your feet - like you can with internal types by fitting a different spindle length.
The crankset you linked to will have its spider shaped to provide the optimal chainline with the SS standard 120mm rear dropout spacing & resulting sprocket placement. (Multi-geared road bikes have 130mm rear spacing.)
Just ride the bloody thing and enjoy yourself!