I co-own one implement, the WC-68 chipper, with my brother who lives an hour and a half from me.
My father and I live beside each other. I bought the Kubota and a few implements for the FEL when he and I started really jointly maintaining the entirety of the property. Deal with him is he can use my stuff like it’s his so long as I can do the same with his 3 point implements, chainsaws, and a short list of other stuff. Keeps us from buying two of everything. Things we both might commonly use are in one or the other of two buildings we both have access to. I don’t co-own anything with my father.
It works for us I think mostly because we all three owned a business together for several years (sold it a few years ago) so we were already pretty well used to dealing with business/money issues. And we’re family, which could be a plus or minus, but 100% love my brother and Dad; know them both VERY well; not kicking either to the curb over a piece of equipment.
Point of all that:
1) I’m fine with co-owning an implement with my brother that neither of us uses constantly and when we do, it’s never an emergency. I also know if somehow I got screwed out of the entire value of the implement it wouldn’t really impact the relationship. Pretty confident either of us would rather fix or replace the whole thing as opposed to returning it broken.
2) I co-own NOTHING with my father. Never have, never will. He retains the option to stop my access to his stuff at any time for any or no reason and I retain the same right over all my stuff. I don’t think that would ever happen, but just a different relationship. We also have a LOT more than one implement involved.
Not sure there is one and only one right answer. With a neighbor, I would probably either not do it or go with the model of each fully owns a list of implements and you share use of implements but not ownership. That model makes it much easier to separate if one of you moves, dies, or it just isn’t working out. Even with that I’d want to have a serious discussion about who pays for MRO on them in whatever scenario to make sure both are on the same page. Only way I’d co-own with a neighbor would be we set up an business of some sort, business owns the stuff, and we own the business.