This is a very common problem in the rules, and I really wish authors would learn to start rewording/reordering their sentences to eliminate this ambiguity.
Basically, it comes down to whether or not the “unless it makes a DC 11 Will saving throw” clause applies to
never attempts to escape of its own volition and agrees to any reasonable request
or only to
agrees to any reasonable request
My understanding is that technically, the rules of English grammar require a comma before the “and” to separate the two clauses if you want the second result. If the authors were lawyers, then I’d feel comfortable just making a ruling based purely on that. But since they are not, and furthermore it isn’t expected that their readers are either, I am very uncomfortable with giving the presence or absence of a comma the weight of rule. They’ve made much bigger mistakes than that in the past.
Therefore, I’d probably just go with that which makes the most sense, based on the cost of the item and how much power it’s supposed to have. DC 11 is really low, so if they’re allowed the save it’s going to make the item rather useless, and getting manacles on someone in the first place is very difficult, so I’d be inclined to not allow the save. On the other hand, no-save incapacitation is pretty potent, even if it needs a set-up.