I picked up a used single seat Ranger and came across the rumble seat for adding extra passengers. Those that have gone the route, please provide your feedback.

https://www.everythingpolarisranger.com/deluxe-utv-polaris-ranger-rumble-seat-by-great-day.html

Good for younger people but hard for older ones to get into.

Looks cool but would rather have it facing forward so riders can duck limbs!
And kinda hard for older folks to get into without a ladder or something

If you haven't bought one yet, you might look on craigslist or facebook marketplace for someone converting a school bus to an RV.
They will usually be happy for you to take a seat or 2 or 7 and they have a tough frame with pads on bottom to bolt it down securely.
Put one on your UTV an use rest for seating in shop, barn, etc.

Dad put one from cabelas in the back of his RTV and it's served us well. It's not as heavy framed as that one, but we've ridden in his quite a few times and we aren't little people lol.

Cabela's Yutrax UTV Jump Seat

as ZK pointed out, we put one of these in the bed of our Kubota RTV facing backwards. Later, I built a high rack and put the seat up on top facing forward. It's probably at least 8 years old and still in good shape. easy to remove and install too by pulling 4 spring pins just leaving the tracks in place.

I have this one in my wolverine and it works fine. I put the kids in it for riding around the neighborhood and did have two adults in it as well. I wouldn't be taking it up any technical trails without a rollcage but flat land it is fine.

I just went to a junk yard and bought a back seat out of a car - bolted it down to the bed of the Ranger - worked like a charm