it is different for all of us.
on the a350 it is very hard to get datas and i do not know how accurate is simbrief. i will check with some real world flightplans and report the difference between pfpx and sim brief.
the lack of answer from a developper for a product that is working is not surprising: pfpx is working and they are fixing the server when there is a problem.
now topcat, it is very simple judith said in the past anybody with the skill to program can contact them i doubt a lot has done it ...