I have a comment or two on the subject. Ive had experience with 4 units so far, maybe my mistakes will help you. I have a Kubota
L4610 (39 HP at the PTO)
First
chipper- BCS BIO100
chipper/shredder, 8HP Briggs cost about 1000 bucks. It lasted about 8 hours before the vibration started cracking shrouds and the Polish main bearings fell apart. BCS wanted 85 bucks for the bearings, a local bearing supply charged 24.00. I sold this turkey as soon as I got the bearings in it.
2nd
Chipper- A clean used Crary Bearcat, 8inch, 25 HP Kohler. It was a trailor mount with a rotating lazy susan (a very cool and work saving feature) This was an excellent machine, purchased used for 3400. I was not happy because I could not pull it over rough ground (low ground clearance) and the chute angle was quite high. It worked well and could easily service 2 people feeding it. I mentioned I wanted to sell it and it was sold just that fast. I regret selling it.
3rd
chipper- Valby 140-(3300.00 delivered), dealer dropped it off for me to try. I ran it for an hour. Very well built, but the slow speed 540 RPM disk can beat you to death. This would be a serious contender with self feed, at much higher cost. I also was not thrilled with the idea of plumbing the remote hydraulic and sharing my Super UDT fluid with another implement. I took it back, but was impressed with its construction. Also the Valby does not make "mulch", but cuts large chips, about 1/4 inch thick
4th
Chipper- Befco Bushmaster 6 inch, mechanical feed, 900 pounds, 4200.00 delivered. I thought I had found the one! Nobody was able to tell me much about it, except it was heavy duty and nobody seemed to have any trouble with it. I ordered on the caveat that if it didnt work I would return it. It arrived well crated and 99% assembled. It ran smooth and very quiet (no howl) I ran it for 10 minutes and then loaded it in my pickup and hauled it halfway across the US to dump it off at the sellers place of business. I got a refund. This is a real piece of Cra-. It would rank with Italian Bio 100 for reliability. Chinese bearings, Korean belts, hundreds of nuts, bolts, pulleys, etc. The mechanical feed is a joke. This would be a mechanical night mare if you tried to use it for more than occasional branches on a small home lot. There are better choices.