Our hospital unionized some years back and things did definately improve for the nurses and techs afterward. By that, I mean, pay was increased (substantially!) to become more competitive with local area hospitals, mandatory OT taken away (a big win) and other things.
I personally think unions can be a double-edged sword. Some believe they perpetuate and even encourage sub-par performance, and there persists a false belief that "you can't fire a union nurse". (it's true you can't, if you don't have excellent documentation, but that is only fair). They (unions) don't really encourage individual performance excellence in many cases, as pay is usually determined by seniority, not merit. Also, they make it hard for a given single nurse who has the skill, to bargain for his or her own compensation and benefits in a particular position or hospital.
Once a shop is "closed" you MUST be a member or you cannot be employed there. There are some hospitals where some nurses are unionized, others not, but these are not as common. Most go "closed".
Having a union rep can be a darn handy thing if you are being unfairly-dealt with as an employee----but again, some people are already very good at self-advocacy and see this as unnecessary, or even an insult.
Yes, there are plusses and minuses, like anything else. Lots of varying perspectives.
I will say this: it strongly depends on WHICH union you ally with, as to how much and how well they will serve you, the employee member. Some are better than others. Some are non-nursing, others nursing unions. It would behoove you all to do your homework before "going union".