The boots help you quickly get back up to a good health level quicker. I don't care if FR will then overheal, I just want more snap healing after getting low. With 3 FR charges and the new 2p healers can focus on saving other raid members as I'll always be able to use FR.
They're also insane for high m+. Might switch back to legs but I got 950 tier which I'll probably use for the rest of ToS.