This is problematic.
An ultra strict adherence to RAW cannot parse "land on your feet," because that term has no rules-based meaning. It's the same as a hypothetical power that read, "and you knock the target over" -- the intent is pretty clear, but the designer who wrote the item somehow used the wrong words to convey the rule he meant to invoke.
Because of this, the RAWest possible reading of the property must discard, "and always land on your feet," and treat it as if it were flavor text, which it isn't, because it's inline with other rule text, in the Property section, rather than in the Description section, where flavor text belongs.
The RAI is exceptionally clear here, and I strongly believe that you should not penalize your players for poor writing by designers.
The mechanical difference between "you land on your feet" and "you are not knocked prone" is that "you are not knocked prone" is an actual rule element, while "you land on your feet" is a ruleless assertion which is repeatedly used in magical boot property text to mean the same thing.
My best (unfounded) guess is that whichever item designer wrote the boots intentionally used different phrasing so as to sound less redundant, but for actual play purposes, I would treat the two as fully interchangeable/redundant, as the writer appears to have done in writing these boots.