I know this question is not directed to me, so please excuse the response!
With the K5, I found the D-BG4 grip really improved the ergonomics of the camera. So, naturally, when I changed to the K-1, I bought the D-BG6 grip. With the larger size of the K-1, the D-BG6 grip is not a necessity but, even with the larger body, I prefer the ergonomics with the grip fitted so much that I never remove it from the K-1. I gifted the K5 to my daughter who does fashion photography with it and she prefers to shoot without the battery grip.
I have large hands and the battery grip certainly helps me to hold onto the camera more easily. I realise that would somewhat detract from the compactness of the KP.
So, very much personal choice I'm afraid!