Join! I'm a member and have used it loads this past year with issues on placement, and as a healthcare assistant, really good advice! Plus you get a discount off the nursing standard, a dictionary and a little badge to pop on your uniform hehe!
Definately join atleast one union during your training, we got to choose from unison and the RCN, and usually they will both do a talk at the start of your year- wait until you've heard their talks of what they can do for you, till deciding?