On the K-5 II I preferred a grip even when using the camera in landscape orientation because otherwise I could not comfortably fit all fingers on the camera's grip.
Shooting in portrait orientation is also much more relaxed with a battery grip as it repeats the main controls and thus avoids arm contortions.
It is, however, very unlikely that I'll ever get a D-BG6 for my K-1. The reason is that Ricoh -- for inexplicable reasons -- decided to
permute the button layout on the D-BG6, compared to the camera layout. In case you follow the link: "Option A" is the brain-damaged (sorry, this still frustrates me) original D-BG6 design with only one out of three buttons in the same relative position and "Option B" is an alternative where at least two (the most used ones) out of three buttons are in the same relative position.
The D-BG4 for the K-5 (II) did not play musical chairs with the camera buttons on the grip and hence I could fluidly change between landscape and portrait orientation without rewiring my brain upon each change.
Despite the fact that I would appreciate the more natural arm positions when using portrait orientation with a grip, I do not plan to get a D-BG6 and somehow learn how to dynamically adapt to the changing button layouts. This would be akin to buying a third-party grip where the dials work in reverse direction. Sure, you can adapt to that, if you really want to, but I had one of those and I replaced it with a genuine Pentax grip as soon as I could. It drove me bonkers.