An unsecured loan just a straight cash loan. In my experience the interest rates are usually a fair bit higher than a vehicle loan, and I would assume the maximum amount is generally quite a bit lower.
In my experience it really depends. You are still contractually and legally obligated to purchase a vehicle in many of these setups, they just don't follow up or enforce it directly in most cases. Loan rates are nothing like unsecured personal loan rates. Probably higher than best auto loan rates. With rates being what they are it may not make as much sense to use an unsecured loan at this point, but when rates are low the cost was negligible and the convenience worth it.