I have DesignCAD and TurboCAD Delux. I use TurboCAD solely to render images of 3D models produced in DesignCAD. It is not a perfect solution. When DesignCAD has equivalent rendering options I will not need TurboCAD.
I have used DesignCAD since 1987, and I am pretty familiar with how it works. Consequently, TurboCAD is very confusing. It doesn't work like DesignCAD in several ways:
1. If it has a gravity snap function similar to DesignCAD I haven't found it (snap to anything, anytime). It is more like AutoCAD,and that is about like designing with a stone ax on the walls of a cave. You can select some things some of the time, and have to constantly fuss with what the program will select. I spend far more time fiddling with selection parameters that I do with the actual work I want to do. Bonehead CAD!
2. It supposedly imports DesignCAD files directly, but it doesn't work very well. I export DWG from DesignCAD and import into TurboCAD, and this works mostly. The main problem is that DesignCAD stores surfaces as a collection of facets, and after the pass through DWG smooth surfaces disappear. You need a LOT of facets in the DesignCAD file (very large files) to get a smooth loking surface in TurboCAD.
3. TurboCAD stores a representation of how things should be and DesignCAD stores a representation of how they are. In TurboCAD (and all "parametric" programs) a hole in a solid is stored as a note to make a hole here eventually when the design is rendered. Consequently, you can select an existing hole (a cylinder through the solid), move it, rotate it, change diameter, etc., and the program does all the rest. In DesignCAD after you drill a hole in a solid the solid is modified, period. If you want to change the hole you have to start over with a new solid and a new hole.
The parametric approach sounds nice and easy, but I find it impossible to predict how intersections of multiple solids, holes, etc. will interact (as does the program). It is fine for simple things, but doesn't always work with complex drawings. For example, a few years ago a review of many $10,000 to $20,000 CAD programs revealed that they couldn't draw a rifle bore (I think most can now)! The interactions of generating the rifling cross section, extruding it into a virtual helical solid, and subtracting the result from a virtual cylinder was unpredictable. DesignCAD could do it because the object is produced in a series of user defined steps, just like you would in a machine shop. At any time what you see is what you get. DesignCAD works just like a milling machine or a lathe. If you make a bad mistake, you have to start over.
Most of my problems with TurboCAD result from my familiarity with DesignCAD and the extreme ease I have creating things with DC. A new user unfamiliar with either can probably learn one as well as the other.