I have a 2000 Tahoe (new style) with the 3rd row seats. They're heavy and cumbersome and mine stay in a spare bedroom closet. But when I need them they're relatively easy to install.
You asked about the leg room...it's not great on these but would guess the Suburban and Yukon XL are better.
The seats are low and your butt sits about 12-inches off the floor..with your knees up near your chest. There is no footwell in the floor in mine.
Access is difficult for adults as you have to fold the 2nd row down. Kids will likely just vault over it.
In other words, they're fine for kids and for adults only on short trips. Installed, there is about one-foot of space behind the seats for storage, but you can fold the seats up for a bit more room.