An analysis of chains and the deals that bind them
Valentino's chain on Angel: Made of smoke; flimsy and lacking integrity. I recall Vox in Radio Killed the Video Star asking Val if Angel had quit. If that's been an option for Angel this whole time, why hasn't he done it yet? The answer is in the screenshot above: it's smoke and mirrors. Whilst the contract itself isn't airtight, Val's manipulation of Angel is what keeps him in place.
Alastor's chain on Husk: Cast-iron; damn near unbreakable. Husk is completely at Al's mercy.
Alastor's chain on Charlie: There isn't one, but we can see how their little favor quite literally forced her hand.
Rosie's chain on Alastor: Also not a chain, instead a leash. Doesn't look particularly strong, and that's because it never really was. Alastor could've backed out whenever, but he would've lost his powers along with it. Instead, he exploited a loophole that made Rosie break her end of the deal and was thus able to retain his powers.
Vox's chain on Alastor: Considering Alastor was the one who proposed this deal, he knew that Vox was going to be more focused on the thick cuffs rather than how laughably brittle the chain itself was.