Product review (5 stars): Very effective
You might be surprised at how much you will remove.  My vent wasn't obstructed, but I thought it might be prudent to try this while I was replacing vinyl venting that had holes in it.
I didn't need to use a drill.  Make sure you use electrical tape as the instructions recommend.  Even with the tape, you can feel the rods wanting to unscrew when you release pressure from guiding them through the vent.