The big question mark for me is: Is it really worth the additional muni cost?
40 mun is not a "huge" cost, but you'll get the normal barrage for free. The first 2-3 salvos will usually land in an area that your opponent will vacate anyway once he knows where the barrage is aimed at, even if he thinks it were a normal barrage. And if he is looking at the front line and notices the Katy hitting unusually close to his troops afterwards, he might just dodge it alltogether.
I've always opted for the normal barrage and put those 40 mun somewhere else.
With blobs, shotgunning your Katy with the normal barrage is still your best bet, but the consistent long range accuracy of the creeping barrage is huge, and it can and will punish team weapon spam. I've noticed it can also consistently destroy or decrew pak 43s behind shot blockers, which can otherwise be a pretty big challenge without off maps.