Pros
I've worked for both unions (local 97 and local 97C) and now most recently I work for management. If you are going to work here, definitely start applying for a union position, while the pay in management might be better, the benefits of being in a union outweigh the salary. Vacation time, holiday pay, sick leave, healthcare, 401K, dental, etc - WITH the safety net of an union backing you. They are working to make most positions hybrid due to the pandemic which supports a better work-life balance. You are guaranteed raises, bonuses, and a living wage increase every fiscal year (which SHOULD be the standard)
Cons
The vacation time compared to similar companies is laughable. My partner works for RG&E (Avangrid) and receives 6 weeks of vacation at point of hire. The most I've received after working for NationalGrid after 4 years is 3 weeks vacation. Seniority Matters: Working in the union means seniority matters for vacation bids, shift bids, and any other job offers. A lot of employees have worked there 30+ years, so unless you're there for the long haul, you will get the worst of what's left over.