Hi Rustabout,
I don't mean to be picky but nowhere in your original post did you mention Revit, you were asking about Autocad vs. Bricscad.
Bricscad as you are aware is based on the .dwg format and follows a similar direction (initially) to Autocad, apart from dynamic blocks it works pretty much the same as Autocad.
Revit on the other hand wasn't originally even developed by Autodesk, so is always going to be different from Autocad/Bricscad.
Bricscad's additional programs for Sheet Metal and Architecture are obviously different from Autocad and Revit and the whole idea from what I can gather is these additional disciplines are all based on the same .dwg format allowing you to have one set of software but work in different disciplines.
Bricsys have their own ideas about how to do Sheet Metal & Architecture, so plough their own furrow in how their programs function.
Once your trial has finished you can still use Bricscad Shape as it is a free program so will give you the chance to carry on trying the core 3D drawing parts of Bricscad.
In respect of purchasing Bricscad, it is all very straight forward, you either buy the software outright or subscribe for a year at a time.
If you buy it outright, you own it and don't ever need to update it if you don't want to. If you decide to take out the maintenance, you get all updates for the year and the chance to update to the next main version within that years maintenance.
I have no experience working with Autocad but have been using Bricscad for 6 years and have found their support really responsive and helpful.
Even if you are trialling Bricscad you are welcome to submit support questions, which hopefully can answer any of your queries.
Bricscad isn't the only Autocad clone out there, there are a few others including Graebert's offerings and of course Intellicad in various flavours.
All this software is based on the ODA's core .dwg functions and if you go to their website
www.opendesign.com, you will see that they are working on Architectural features and the Revit format as well, to further integrate other formats into the .dwg fold.
Hope that helps in some small way.