[1] The headword (extracted from the quotation given) is neuter nominative/accusative plural of the adjective kai/rios; cf. kappa 1187, kappa 1188.
[2] Sophocles, Electra 226-228 (with scholion); the Suda leaves out a)/n after pot'. With a less stilted rendering of the ethic dative: "Who indeed, my noble friends, who that keeps what is appropriate in mind, would think any word of comfort right for my ears?" (Sir Richard Jebb, web address 1)
[3] The scholiast paraphrases the verse as "from whom would I ever hear a word of comfort?". In that context "advantageous" is glossing pro/sforon, "serviceable", and not kai/rios.