I use Fsbuild along with Topcat for most of my fuel and flight planning now. It took a bit of fiddling with cfg files etc to get the data in-putted to match up with what the computer (CDU) in PMDG 737-800 was outputting. I know you can just use the CDU to get all those figures and sometimes I do just that. However I prefer doing it this way because it is more realistic. It feels like a proper dispatch has been created for any given flight.
Today I put a flight together from EGCC (Manchester UK) to ESSA (Arlanda Stockholm). The preparation to set my desktop with all the correct hardware and the flight planning takes me about 20 minutes in total. Great flight that went without any problems apart from feeling rushed in the landing because the wife and kids were waiting for me to go out somewhere.