This isn't exactly unbiased, as I am a volunteer steward for my union, but I also spent 13 years in management, so I do have both perspectives:
And I note the thread is pretty old - sorry you didn't get more helpful advice - you've likely made your choice already, but I'll still throw this out for what it is worth.
In most unionized hospitals, the top management makes sure their frontline managers are compensated significantly better than the staff nurses, so when the union wins a pay raise, you tend to get bumped up automatically.
if you are a manager who likes to "fly by the seat of your pants" a lot, then the rules and procedures in a unionized environment can seem confining. They can be really confining if you like to play favorites - give your special friends special privileges and the like. But if you are basically fair minded and apply the same sort of documentation to management that all of us apply to patient care, you won't find it a big bother to have a few rules around. As the chief steward at my hospital, there are a small handful of managers with whom I have frequent conflict, and the vast majority I never need to talk to.
Really good managers often learn to use the union contract to their advantage in dealing with their own superiors - when your boss asks you to do something really dumb that will harm patient care and **** off your nurses, you can say " Won't the union give us trouble over that?"
The old canard about the union protecting bad nurses is mostly false. A union contract gives nurses the right to a fair procedure in disciplinary action, but that just means you have to have the discipline to have your ducks in a row, so to speak. If a nurse is being a problem, you need to let them know how they are failing, give them a chance to improve and document that they fail to improve before you take action. Managers who say they can't get rid of the rare genuinely bad nurses "because of the union" are really just saying they are too lazy to go through the proper procedure and do the documentation they need to do.
Anyway, hope you made the right choice for you and it worked out well.