I would wager than at least 90%, if not 95% of the worst accidents are hydraulic feed wheel chippers.
Here's the safety lesson in a nutshell, "This is called a Chuck and Duck, not a Chuck and watch it eat and get the shit beat out of you by the brush coming through here. Feed from the side, flowing out of the work area, don't turn back into the work area, where the next guy will be coming to feed it. Feed it using the big steel shield as a big steel shield. Do not put your hand within the feed chute (beyond the tray, where it tapers). Repeat 1) chuck and duck (not run like hell or anything), 2) use the big steel shield, 3) don't put your hand where it can be crushed between the wood and the steel chute, as with the general overarching rule of don't put yourself where you can be crushed.
Mine is 9x16, telescoping and swiveling round chute with deflector. The entire chute also raises and lowers.
4400 pounds. I move it all the time to the brush with the mini. Greatly cuts hauling chips, leaves the chip bed open for wood or nothing.
Chrysler 318LA (light industrial, IIRC) bulletproof v8. Chipper made by Wayne, 1975. Wayne and FMC were/ are connected. They make a lot of stuff, including garbage truck compactor rigs, and other big equipment.
It eats! Tough enough for the mini to feed it. Needs more finesse than with a hydraulic chipper, I reckon.
On flat ground, I can move it by hand. Very little tongue weight, like a 100-150 pounds, very balanced on the axle. I can lift it and spin it by myself on hard flat ground, with some grunting. Two guys, for sure. Using chocks to your advantage, you can do a lot to position by hand on a hill.
I've had that chipper since 2007. The hour meter has been on 3800 for at least 7 years. I put a new muffler, hand paint, lettering, 2 used tires, a plastic fuel tank after sediment problems. One clutch. blade sharpening. Tabs. Some carb work a couple times, in part due to the sediment in the old tank. Alternator. Starter. Misc. this and that. $2450 purchase price plus maybe $2-3000 in parts and pro labor, plus my labor.
Pretty much runs better than when I got it. Starts without issue.
I think I could sell it for 3500 pretty easily.
Likes fir limbs, maple, alder, hemlock.
Doesn't like dead so much. eats dead better tip first.
Doesn't like madrone's twisty nature. Oak needs more pre-cutting. Again, twisty branches.
Keep it sharp. Feeds fast.