I'm familiar with the Bullworker and would say the main drawback is that it leaves you no room to up the level of your workout.
I understand that it may work really well for some time, but, unlike weights (either machine or hand held) it gives you no opportunity to really increase your resistance.
Therefore, great to start, but I figure after some time you will just be at a plateau with your fitness, because you arent giving your body a new and harder challenge. So there will come a time when you feel the need to do more.
My step dad had a bullworker back in the mid 70's and I used it to work my pecs - it did give a challenging work out for a time.
Start BF 38% Goal 25%
5% - 200 -
165 for cruise December 2012.