A Use Tax is a tax on the Transfer of Title. First of all the mower is not allodial in regards to property that is impossible, unless you are a king. It is allodial in terms of estate as a Fee Simple. The mower is a THING. The Use in the Thing is to cut the grass - typical use.
Now if I am holding the Thing for my own uses in possession and I let it out to you then a TRUST forms.
You are Trustee holding the mower in Trust upon your uses for a time and you might benefit of its uses as a third party, but I have beneficial interest in the Trust because I had the possession and I TRANSFERRED it to you for a short time.
The Use in the Thing is an Estate. And since I transferred the FEE via Lease or Deed, you now have a Qualified FEE.
Perhaps the lease was a friendly loan - nevertheless - you would be entitled to the return of the full use of the mower [thing] upon your demand. That is unless you settled on certain terms. Then you must abide in those terms - covenants - such as creditor/debtor relationships.
Regarding Roy and Bob - Bob is Surety to the one he contracted himself to - Roy has no duty to assume the Surety UNLESS Bob stipulates that in the Contract he has with Roy. Bob would be a fool to let Roy use the Thing absent an agreement [typically in insurance - third party].
Roy makes a USE of the THING. Roy has the actual possession but Bob has the Right of Possession. Bob Promised in Contract to another to be Surety. Roy never promised [he was not a party to the Contract] - therefore has no liability in Bob's Contractual obigations. Bob would be a fool to let Roy fly absent a Surety Understanding the Use whilst the Thing was in Roy's Possession.
The Lender [Bank] requires the Borrower to keep insurance on the Thing [house] whilst the Borrower is with the obligation - meaning the Borrower might lease the house to a tenant - or he might actually reside in the house [thing] for the Use consistent with Residential Property.
Regarding Use of Property belonging to another - SPOT ON. The Cestui Que Use [he who created the Use] wants a Return from the Trustee. You are spot on.
Shalom,
MJ