While I have no experience with a PTO type
chipper, I can give you my thoughts in general...
A
chipper is not a mulcher, even though what comes out can be used as mulch. Small stuff, while it may not clog, will have a hard time feeding. Throw your small stuff in on top of a leafy or dense wad and let it get ground up with the big things.
Always stand on the side of the feed hopper, don't stand behind it. A limb can become a large baseball bat and give you a mighty whack. In the Wallenstein picture gallery, the demonstrator is doing this exactly wrong. He is standing in such a way that he could easily be injured if the limb gets away from him. I can't tell if he's trying to push the work into the chute or not. Let's hope he is just supporting the limb to keep it feeding.
This Wallenstein thing is a "chuck and duck" type, so once the object goes in, that's it. No way to reverse the feed. This requires extra caution as stuff can get flung backwards out of the hopper. Maybe right into your face. If you can afford the hydraulic feed chute, buy it. It is a huge safety margin, as well as making chipping less stressful. With my Bandit, I can just place a tree in the hopper and then use the hydraulic feed to control the feed rate.
Wear eye and hearing protection as well as a hard hat. Keep people away who don't know how to use it.