I'm not really a fan of either, and I really don't like that Kensei is a monk tradition and not a fighter as it was in 2e (the only time I used a kensei)
I think Kensei as a theory (being a person so attuned to one weapon it becomes an extension of themselves in a spiritual way) fits pretty well with monk. That said, one of the more cogent reviews of it points out that this version of Kensei breaks with many of the aspects that previous editions have held on to at the very core (focuses now on multiple weapons, rather than 1; only get the AC bonus when wielding the weapon if you make an unarmed attack; etc etc).
Way of Tranquility I like, I think it could be useful. One of the major complaints I saw was that the healing they can provide is a boosted version of the paladin's Lay on Hands feature and it removes some niche-ness from the Paladin because of that.
Kensai is interesting, but more thematic than useful (unless I'm missing something?). Way of Tranquility seems like it'd be great for an NPC, but unless you have a game styled in a way that would allow peace to work, it seems unusable.
All I remember about D&D Kensai is how ridiculous and broken they were, if really cool thematically. I fully accept breaking away from past versions, though. Tranquility looks really good. Double Lay on Hands, and you can mix it in with your attacks? Nice. I agree that it wouldn't work in a murder-hobo game, but it should be able to find its uses in most others.