I had an untinted (apart from standard) 9-5 estate and now run a tinted citroen C5 estate. Second hand so it came with it I didn't ask for it.
Advantages, looks cool, maybe keeps some glare out on very brights days. Looks great after a wash if you chamois the windows. Disadvantages, too dark for normal days in this country, makes it hard to see when reversing in the dark, other drivers can't see through from front or back. Harder to see exactly what's following you at night. Bikes can disappear from view in the dark.
On balance the disadvantages outweigh the advantages in everyday uk road use, for me, but its a personal thing. If a car comes with it fine, but I wouldn't pay to get it done.
Hired a Chevy equinox in the states last year, by chance a top spec one, had very dark rear and rear sides, a liability. Couldn't see to manoeuvre at night or in enclosed car parks. Fortunately if you pressed the right button the radio screen relayed a picture from a camera in the boot lid otherwise I might have been parking by ear.
I had some grey mesh shades with a single sucker in the middle when children were young, just blooped it onto side windows when needed. Cost a few shillings.