I also import models available in both FBX and OBJ format with SimLab...
SimLap does a great job, but you will need to cleanup the models to reduce the size and make them usable in many cases...
You can benefit by installing the CleanUp plugin by Thomthom...
Please note that some models will take very long time to cleanup...
(by very long time, I mean 3-4 hours!
The plugin will estimate how long time it takes to cleanup a model, however, these estimates are usually never correct... Models are usually cleaned up a lot quicker then what the plugin have estimated...
Hope this can help you further...!?