If you have 'super low' rates, that implies to me that you may have mortgages that were extended to you as primary residences. I guess that's a question, since I'm not aware of super low rates on investment property. So, anyway, I can tell you this, flipping the deeds from individual name(s) to an LLC will begin two balls rolling that can really take you down. One is if any clause exists in your mortgage that identifies the property as excluded from use as a rental. Most do if presented as a primary residence, to which you signed an affidavit at least twice..once on application and again at closing. If any of this is true, then the mortgage company can call the loan due the minute and second they discover the LLC ownership and it's purpose. The other problem that surfaces, and perhaps first, is when the insurance company submits to the mortgage company a request for payment of the property coverage (even if they knew all along it was being rented and the coverage was a landlord policy). The policy invoice will reflect the LLC naming, not the naming that is on the original mortgage documents. This puts them into a tail spin and they usually will throw the invoice away. After not getting an invoice that reflects what they are looking for (correct name per their records) they assume that coverage was dropped. This starts a series of nastygrams coming at you and a whole lot of phone calls back and forth that may or may not end well.
Consider your moves carefully. Talk with a lawyer that has successfully done what you want to accomplish and has dealt with all the gotchas. There is another way that can work in certain situations, and again, you will need the advice and counsel of an attorney that knows this stuff from experience....a trust. It may work as an irrevocable, it may be revocable, it may not work at all in your state. In any event, it would still be work to keep the mortgage company in line since names on deeds and policies will change.