Been to Bong several times, although not for dirt biking. They hold model rocket launches on several weekends out of the summer, and the launch site is right near the riding area.
I've seen the "trails". If you have an ATV and it's your only riding option, go. They are wide open loops, not a tree to be found. Probably okay for a beginner, as well. More experienced riders would get bored quickly.
If you decide to go, call ahead. The trails can be closed or limited due to weather or special events.