In my last post about Step Forward Paper, I somehow forgot to discuss show through and bleed through. Unfortunately, I disposed of my sample paper so I cannot use the same sample for comparison. From my memory, there was very minimal show through. I do not recall any bleed through, and if there was it was minimal and only on the very wet and thick black ink. The concern for many is writing on both sides of the paper, and my recommendation is that YES, one can definitely write on both sides of Step Forward Paper with a fountain pen.
I did a quick test below with Sheaffer Black ink in a vintage fine point Lady Sheaffer.