Not used the CARES harness on Delta but on a range of National airlines and Low Cost Carriers between U.K. and Spain and Japan (indirect long haul).
Whilst it didn’t actively interfere with the table and functions of those sitting behind us, I’d say it does compel you to engage in a polite explanation and request for cooperation with whoever is affected. Selecting seats at the back of the cabins eliminates this.
Another thread here -
Any experiences with Kids Fly Safe Cares Airplane Safety Harness?
The harness is fine when the child is awake but might require you to actively support the child’s head/shoulders if they fall asleep, but thats for take off/landing and when there is enough turbulence in flight to merit more than the standard seatbelt (between Beijing and Tokyo is notoriously bumpy).
I don’t drive and avoid situations where I would need a taxi (I’ve never used Uber or any similar service). The CARES belt was ideal for us and, once our kid had grown, we passed it on to friends.