If you need tunneling prevention, one option is to use the CCD motion clamping in btDiscreteDynamicsWorld. See also Bullet/Demos/CcdPhysicsDemo.
You can use an embedded sphere that prevents tunneling, using the following settings:
body->setCcdMotionThreshold(0.5);
body->setCcdSweptSphereRadius(0.9f);
Add a camera zoom setting for the demos, thanks to ejtttje, fixes Issue 543