As a developer of small-scale model trains, especially ones for public consumption as free models, CSG is an important feature to create the complex shapes required of the models as well as optimizing the models for decreased brick count.
The issue is that CSG V2 creates size offsets that are quite noticeable compared to CSG V1.
Take this piece of a locomotive:
All the parts are built on a grid of 0.05 studs. There is a tiny tiny gap between the stairs and the part with the red sides, which is extremely aggravating. In fact, the tiny shifts in sizes and positions continue happening even at 10x the scale.
Below are the aforeshown part, scaled up 10x. The one on the left was created with CSG V1, and the one on the right was created with CSG V2:
The V1 part is sized as expected. It’s width is exactly 13 studs. But the V2 part is sized oddly; its width is 13.065 studs and its position shifted by 0.001 studs on that axis. After some testing, I’ve determined that the cylinder piece is creating the issue, somehow. Whether I CSG the cylinder before unioning the rest of the parts, or union all the parts in one go, the result is the same.
EDIT: Although the cylinder creates the misbehavior in this small example, there’s larger issues. When the part is rotated 180, translated along the axis, and unioned with the other one, it still creates offsets in size and position.
Here is the two parts for inspection:
CSG V2 problems.rbxm (136.2 KB)