After a decade of experience with the Valby two stage, I have to agree with the post above about the benefits of hydraulic feed.
The one I have is 8" capacity, though I rarely ever run something that big through it as I am doing most of my cutting for firewood. The stuff I am running through it is often beech or other hard woods, or the slash from pine spars and orchard trimmings (ie dead, sharp, knarley, hard pieces).
One thing I noticed early in my chipping "career" is that a longish, knarley piece feeding into the anvil and knives will have a nasty tendency to spin in the shute as it feeds. This alone makes the hydraulic feed a real joy, nay one could say, a necessity!
You have not experienced the true joy of running a powerful
chipper until a branch being fed into the shute pivots and smacks you upside the head as a last belligerant act of resistance.
The other true benefit of the HF is that if you are running a LOT of material through the
chipper, evenutally it will get jammed up. Once one becomes familiar with the signs that this is about to happen, being able to reverse the feed can be a real time saver.
Often the thin green stuff (or foliage), conspires to build up in the exhaust shute to the point where the flywheel fan cannot keep up. If you keep feeding, you get a pretty good blockage that requires shut down and shute disassembly to clear out the jam.
By watching the material leave the exit shute as you feed, you can get a sense for how well the material is moving. The beauty of the HF is that when things begin to plug up a bit, you reverse the flow, clearing the input shute and put a dry, stout, foliage free branch through. The
chipper creates nice dry, large chips that blow out the exit shute quite effectively.
Done right, you can go all day chipping a huge pile of slash and not have to stop for a jam.
My opinion is that cheap tools are way more expensive than premium ones....
Better to by a used, well made tool than a brandy new piece of junk, even if you have to rebuild and or replace the "wear" items.