The recline boot is only used RF- the foot is never used RF. Two different things. There's the boot- the separate piece that attaches for RF- and the foot- the pull-down little piece in the front that may only be used FF. Does that make sense?
If you still have room (and you may with 2 Radians in there, the Keyfit is pretty narrow) it's fine to put it in with LATCH- just make sure that you can still achieve a properly tight install on the center seat. But I find the Keyfit very easy to get tight, usually. Remember that you can twist the buckle stalk down up to 3 full twists (although in the Corolla often 2 1/2 is as much as you can get) to shorten it to let you get more slack out of the belt if needed. And you only check for movement right where the belt goes through, and if it moves less than 1" in any direction when pulled right at the belt path with one hand, you're fine.
If you still have room (and you may with 2 Radians in there, the Keyfit is pretty narrow) it's fine to put it in with LATCH- just make sure that you can still achieve a properly tight install on the center seat. But I find the Keyfit very easy to get tight, usually. Remember that you can twist the buckle stalk down up to 3 full twists (although in the Corolla often 2 1/2 is as much as you can get) to shorten it to let you get more slack out of the belt if needed. And you only check for movement right where the belt goes through, and if it moves less than 1" in any direction when pulled right at the belt path with one hand, you're fine.