I do not especially love the manager.
I almost never use my manager for work orders, though I do appoint one, primarily so I can control who works at specific workstations. That function's quite important to me.
If I need 1-10 of an object, I can queue that through the workstation with very few keystrokes, if I need 11+ of an object I probably need a LOT more than 30... and setting up many sets of manager orders seems to take a lot of keystrokes for me.
So instead I usually place a single workstation order (or a single order on each workstation I want working) with repeat.
If I don't want my last X to be used for production, I first place a stockpile for X in some location, then forbid the items placed in it; forbid and forget, until that mood happens which calls for X, which I can then mercifully unforbid. My repeat orders will use up all the unforbidden X if they can, and that's what I expect and understand will happen, go for it.
For me this is fast and easy, and combined with limiting the skill level or name of who can work at a station as well as possibly a well specified stockpile surrounding that station, gives me great control over what's being made and adequate control over how much of it is being made.
The very rare times I want 11+ of something, but not 'all that can be made', I have usually chosen to fill up my workstation with 10 jobs, then a bit later check and add more as needed. Works for me, rapidly and easy.
The two changes that would encourage me to use my manager frequently would be either to set any number of repetitions through him, OR a set of 1-2 keystrokes that would allow me to tell him to repeat the exact previous order, as well as a way to either specify which of a type of workshop was allowed to receive those jobs, OR a way to exclude a specific workshop from receiving any of his tasks.