A Celestial Warlock using True Strike is only kinda okay, and only when it's competing with two attacks. The two points in its favor are that it's in the Revised PHB, so there's no question you can take it, and that you can potentially skip Blade Pact entirely. Edit: Three points. It works with ranged weapons, though at that point you have to seriously ask why you're not just taking Eldritch Blast.
If you want a non-standard Celestial Bladelock, what you really need is Green-Flame Blade. Not only does it add d8s instead of d6s, but it has automatic cleave damage on a hit. Cleave damage that Agonizing Blast will add to, because it applies to every damage roll.
A Celestial Warlock who takes Blade Pact and substitutes Agonizing Blast and GFB for Thirsting Blade is, at least on paper, a strong build that overcomes the downsides of only making one attack per turn. Especially if your DM runs the sort of encounters where you can activate the cleave regularly. Any build using True Strike is far more narrow and gimmicky.