We have bought the iRobot Roomba S9+ vacuum and their Braava jet m6 as a bundle. Worth having a look for black friday deals!
Hair: Two adults with long hair, normal short haired cat. Very effective with human and pet hair (the vacuum is on a schedule to go around three times a week and the floors are immaculate).
Noise: It's great, but far too loud on wood floors for me (though I am v.sensitive to noise, and you could put it on when you leave the house). Absolutely fine on maximum power on vacuum setting. It's much quieter than a normal vacuum cleaner - when it goes back to the base it's pretty loud but it's a very quick whizz to drain the internal bin - 15 seconds or so.
Falling down stairs: the roomba has a sensor to stop it falling downstairs - like a little camera just underneath the front, and when it moves if it detects there's no floor it just backs up a bit until there is.
Suction etc: you can choose different settings.
Charge: charge works plenty well enough for three bedrooms and a hallway upstairs. When we had it (briefly!) downstairs it was good enough to do 6 different rooms, never had a problem with charge at all.
Cons/notes: It works best if you have zero clutter on the floor. I do mean zero. When it sets up the "map" for the first time you can scoot everything into the centre of the room so it finds the edges, and then you're good, but generally it doesn't like finding new things. We have an alarm to remember to move any loose things onto beds etc. You can set up "no go zones" for pet food bowls etc, but you set those up after the first mapping run. It takes a little while to settle in.
I was highly sceptical of both, and I wouldn't go back.
And btw the mop is amazing. I tend to whizz around with a normal vacuum downstairs and the mop is on a schedule that does high traffic areas three times a week. You just have to fill up the water/cleanser tub inside. Easy peasy.