I think it's great... then again I am SoEzzy so it's my calculator, it's also posted here in other forms and on other forums.
AKA SoEzzys catering planner.
The latest version was 3.06 it is pretty accurate straight out of the box, but if you want to tweak it after you've tried it out you can do.
If you want to spend all the time deconstructing it to build your own, there's no one to stop you, but as wheels go for the average Joe it's about as good as it can be and stil cover the basics.
There are things I'd change when a new version is due, at the moment the ribs are set as 1/2 a rack / person, but you can do the rib calculations based on ribs per person B25 allows for the reverse calculation.
There are lots of folks that think it does a good job and who use it from time to time, but if you've got a better wheel that will work country wide, I'd be interested in seeing it.:-D