Generally speaking, servicing is no more headache than collecting the rent.
Compliance will depend on your state regulator. Make sure you understand the system for regulation in your state, which may vary depending on what kind of lending you are doing. There are dollar limits and lots of rules that you must follow, but they are mostly not a big deal and/or part of your setup costs (e.g., getting all the required disclosures as part of your paperwork package).
Benefits over 3rd party financing:
(1) You said it – autonomy over approvals. Your target market may not qualify for a loan.
(2) You set the finance charge (which can make things affordable for your tenant) and/or you can make the deal fit the situation at hand.
(3) You keep the finance charge.
(4) You can modify the loans without a third party in the middle. Say the home needs [any major repair] after [a number] of years and tenant can’t afford it. You can adjust the loan and front the money. Or say your tenant is about to lose the home because they can’t afford it. You can extend the loan and lower the monthly.
(5) You have so much more flexibility and control without a third party in the middle hassling you or your tenant. It is just simpler. For example, if your tenant is going to lose the home, you can decide when/how to encourage a (relatively) painless default if it’s just not feasible to work out.
(6) 3rd party lending may (e.g. 21st Mortgage will) want you (park owner) to guarantee the loan, so you’re effectively lending not just the money for the sale (which is what you’re getting back) but also the overhead of the loan origination process. And you are left holding the bag if the tenant defaults anyway.
(7) The tenant doesn’t have to pay the overhead of your 3rd party for origination, servicing, etc.
(8) There may be some insurance benefit.
(9) You will be hard pressed to find 3rd party lending in the first place.