There was absolutely nothing wrong with the old layout, so why fix it?
I happen to be in a position where we have 2 shipstation accounts, the first in the old layout and the 2nd stuck in the new layout.
Hands down, everyone here hates the new layout. The old layout is far superior in our opinion.
Did you just nee something for your developers to do? Or what was the deal? Seems to me, and everyone here that has used both layouts, that it was fixing something that didn't need to be fixed.
What EXACTLY is the benefit of the new layout? Please tell us so that we can see if it actually is a benefit or not.

