Choose your Super Hero: Grid Splitter or Kompressor

Guys, I am torn between two concepts for master-detail: "Grid Splitter" and "Kompressor". They sound like the villains from The Running Man, I know, but other than in the film, this time we want one of them to become an actual winner. Sorry Arnold.

Grid Splitter is the concept that shows a header (parent) grid together with a lines (child) grid in one view. Kompressor only shows one grid at a time and compresses the top grid into a single summarized row when the bottom grid is activated. This way the user is not distracted by the header grid while working on the lines, which is in fact a variant of the progressive disclosure interaction design technique we already used to hide the lines grid while working in the header grid.

You can view an abstraction of their behavior in these diagrams (1 & 3 show Grid Splitter, 2 & 4 Kompressor) but perhaps it's easier to go through a scenario for the new concept (Kompressor). Use right-arrow key on your keyboard to flick through the scenario.

Choose your favorite super hero now!

If my doubt persists, I will have to take them to the streets, for some serious usability testing. There can only be one winner.