Silo is good, fast modeling. It has helped me to make a living as a 3d modeler in illustration, jewelry and 3d printing.
The interface is very clean and all the tools and their functions are in the menu bar, not hidden away.
Also, the keyboard and mouse shortcut editor is one of, if not the best ever created.
The modeling tools are context-sensitive meaning extrude, bevel etc. will work across vertices, edges and polys, which is great. And the numerical editor might be Silo's greatest strength if you are doing precise modeling.
Now that Silo is 64-bit, you can import and export huge meshes, as much as your ram can handle. There are no import/export poly limitations.
There are some negatives however. The bevel tool can't do rounding, booleans will crash, there is no local rotation, no perfect circle tool, no deformation tools (taper, bend, etc.), no smoothing groups, no ABF unwrap, pack uv won't work on multiple meshes, surface snapping is view based, .STL export creates huge files, extrude and shell sometimes skew faces badly, the sculpt mode has a lot of bugs, no GoZ or .FBX, no SDK, and the pace of development has been notoriously slow.
Overall, it looks like the current development is alive and going in a positive direction though. I suggest you try the demo from the Nevercenter website before you buy it.