Yep. I’d say look for a new one every four or five levels or so because all the different ones will do is raise your health. Bullwark is pretty generous with the shields, so you could do it every 2 or 3 if you wanted to.
I got it from the second time I killed him (first time was the mission). I started from the lodge, picked up a vehicle and farmed him. I would said it took 5 minutes start to finish.