even if one says; even putting it (a certain way)The meaning depends on the verb and kanji: 言っても means “even if [someone] says,” while 行っても means “even if [someone] goes.” In 控え目にいっても, it means “even putting it mildly.”
JA: 控え目にいっても、彼は愉快なやつではない。
EN: Even putting it mildly, he isn’t a pleasant guy.