And it's such a non-issue, too. It's effectively 2 Ki for the 1st level Inflict Wounds, with +1 Ki per level of upcast. Standard 1+level ki costs.
And there is no verbiage about "seeing the result" before choosing how much to spend. Paladin's Divine Smite doesn't let you see the result either - it just triggers on a hit, just like Shield. Things are only applied after seeing the result if that is explicitly stated.
So we have a non-broken, bog standard Ki costs for spell equivalent, then discussion that is continuing even today that maybe you know if it saves or not before pumping in more Ki that it does not say anything about. * sigh *