Iâ€™ve been using the D-10 databack and P9 grip together â€“ they do both fit at the same time and do not get in each otherâ€™s way at all.
For handheld work I find that the D-10 is a little too thick and that I canâ€™t press my face close enough to the viewfinder to see the whole frame comfortably, so I tend to switch the backs over when I donâ€™t need the exposure data recorded (my nose is of regular size, if that is any help!!).
If you want to keep time or exposure data then it is obviously very useful â€“ and beats keeping a notepad around. It also provides for interval exposures.
The main issue I have with its operation is that it takes time to record the data on the film, particularly on the first two frames when rewinding (about 20 seconds). You can switch off this function, but it is one of the backâ€™s most attractive features. Also, it does not record the film speed which you have set, which seems an oversight to me.
One other feature that is missing is the ability to download the data to a computer file.