I run a belt driven WoodMaxx 9900 chipper, I’ve never had the belt slip or had a jam, the variable speed two large infeed rollers, and 9” opening just eat anything that is fed into it. US made, great support from WoodMaxx. In the event of an issue, I’m more comfortable with belts than direct drive. Although I will say that WoodMaxx have a US made pto shaft that has a shear bolt, I’ve never sheared a bolt in regular operation but have done so while clutching in pto at too high a rev setting or trying to deaccelerate the engine too fast when the chipper had too much momentum. Once I got use to it I have not had issues but it’s good to know that the driveline protection works well when you operate outside of normal parameters.
I would not buy a direct driven chipper, belts offer another level of safety if a problem occurs.
flywheel speed is important as are the number of knives fitted..