I use Aviation W&B Calculator. It was a couple bucks from app store. They have lots of templates people have made. You can make your own using info from POH or edit one that you download.
I get numbers close to POH, within error of reading small graph paper from 1979.
I don't....I use GP. fltplan is typically good enough for the average Cherokee but with the extra seating and cargo area up front, was wondering if someone preferred one over the other.