Slicer reports 1000s of errors not seen in Cura; Render is missing big chunks
Cura and Slic3r are very different programs. You will not get the exact same print between the two. I find that of late slic3r will try to fill holes when older versions do not. So even versions will not behave the same. I will say I have less issues with simplify 3d, but the price is very high.

Following. When this happens I attempt to repair the model. There is obviously some unresolved issues in the model. I use Netfabb which has been exported to this online tool.

Really though. I would ask for my money back ;-)