Know the Angles is for Quivering Palm and the ~+10 damage. While it's true that 10 Melee Power from a fourth Henshin core is more DPS than that, KtA bumps my Quivering Palm into the 80s, and at that point it is pretty effective. Insta-kill > a little more DPS on the mob. And Harper has melee power in it, so you could get up to 3 MP along with KtA for 10 AP.
KtA also allows me to use standard CC like trip:
10 base
20 item
6 insightful item
4 quality item
3 past lives
2 tactics feat
4 Astral Scion
6 Legendary Tactics
10+ KtA
-----
65 base to any tactics check.
8 base STR
7 tome
2 ship
2 litany
2 completionist
1 exceptional
8 augment
2 augment or potion
5 Primal Scream
4 Tenser Transformation
----
41 = 15 STR to tactics. Higher with Shop, Yugo, any real STR items, or STR investments.
That puts even standard tactics at 80+ DCs on a dump STR character. Before the Jade Strike boost, Trip was my CC for golems, constructs, and undead when Jades failed. Coupled with Unbalancing Strike, Trip was actually quite effective. Now that Jade Strike and Tomb of Jade are much more useful, this CC effort is not as needed, but why not have a backup CC in case the others fail?
And, of course, there are certain targets with saves over 100, so you'll actually need KtA to be able to land your Jade Strike or stuns since for those you need to reach 120 for no-fail.
Personally I think Know the Angles is worth it.
[EDIT] - I missed people asking if Know the Angles works for the Jade line. It does indeed. Anything that is helped by Tactics in any way is helped by KtA. That means the Jade Line, Dismissing Strike, Stunning Fist, Dire Charge, Unbalancing Strike, etc. Hopefully they'll add tactics of some form to the DC of all monk abilities.