I have never stayed with a company for a continous stretch for 2 years.

So I say go. Learn, achieve, become, get more pay.

I always look for a challenge and something that makes me think more... these types of jobs have the side benefit of moderate to nice pay.

Never worked in a union, have done plenty of contract work. Unions have their place, but quite often they act as a glass ceiling for younger workers and/or an additional drain on paycheck and/or drain on morale (victim mentality... not all just too many).