MARK -
I used StairBuilder from Theometric before it was purchased by Cadimage and found it vastly superior to the stair builder in ArchiCAD. Having said that, I should also tell you that I upgraded DoorWindow builder, also a previous Theometric product, from Cadimage in the beginning of January. After upgrading, DoorWindow builder crashed ArchiCAD each and every time I entered a value into the objects height dialog. I emailed Cadimage three or four times over several weeks and never received a reply.
Because I had no backup copy of the previous version of DoorWindow builder I was forced to use Graphisoft's door window objects found in the new Special Edition library and found them to pretty flexible, the only bug being that I was not able to make a dry wall return to the jamb without faking the jamb extension dialog by entering a very tiny value just above zero.
I would suggest that you take a look at the ArchiStair plug-in by Cigraph. They seem to be a very reputable company of componet software. I have not yet used ArchiStair, however, I will shortly, on the current project I just spoke of.
ArchiCad 21 / OS X 10.13.5 /
iMac 3.2GHz i5 - 32GB /AMD Radeon R9 M390 - 2048 MB/
Dual 5K - 27" Displays