The electrician I hire regularly (he is almost full time here) works for a Union and is assigned to companies. He technically works for and reports to the company, but the Union signs his check.
He gets 0 paid vacation days and 0 paid sick days.
When work is low, they limit them to 20 hours a week so the Union doesn't have to pay benefits (his words). Thankfully, I have enough work that I can allow him and 1 or 2 of his guys work when it is slow to help them out, but even I have times where I cannot help. I hire him and his guys because they are very good, not because I am a bleeding heart, so a ploy to get hours from me does not work, if that is one thought you may have. Once our punch list is done, they go home.
Their retirement system traps them into staying as well, as they will lose 100% of their retirement benefits if they leave the union and go private. For most guys, they are too far invested before they figure it out. My 401K is by far more valuable than his pension after 30 years, compared to my 25 in private industry.
Outside of training, his union provides no benefit whatsoever. Many of the union guys change companies like underwear just to keep working and making a living. That sounds like a miserable life to me.