They serve completely different purposes, from what I understand. We have a Roomba, which is a vacuum only. It works reasonably well, better the more often we run it. If you generally keep a very neat house where things are rarely out on the floor, you can easily run it every day, and it's a good option. We have little ones and we end up having to put a bit of time into picking up before running it, so we only run it like twice a week. Plus it is quite loud, so it can be hard to find time to run it when it won't be disruptive. It can get stuck on/under things like the edges of rugs or under furniture with legs of a certain height, so you have to figure out how to work around those or be there to pull it out when it happens.
The Scooba serves a different function. It washes your floors, with soap and water, and I believe it's not recommended for hardwoods, which we mostly have. I don't know if it also vacuums. We did look into the iRobot model that is supposed to dust hardwood floors, I think it was called the Brava, but you had to constantly replace these Swiffer-type cloths and I knew that would be annoying for us.
SO bottom line, if you have mostly hardwoods, I don't think the Scooba is an option. I think there are some other vacuum robots that have come out in recent years that get good reviews, which I would look into before buying another Roomba. Not saying I wouldn't buy a Roomba, but it does have some flaws that can be frustrating and I'd be interested to see if another brand might work better.