After my 562 started having problems with a wheel, I could have fixed it but I figured it was getting a bit old and I might as well look at upgrades.
The 780 is my 5th roomba in 10 years. It honestly seems similar to my 562 and 580, although tests say it's supposed to pick up dirt better than them. It looks a bit more fancy but actually comes with a smaller dirt bin and filters you cannot self-clean/wash anymore.
It still has weak suction and fails to pick up anything between my kitchen tiles, but it works well on carpet and hardwood floor.

Functionality honestly looks much like my 580 (actually, the remote is not RF, and Irobot cheapened out and removed the extra dirt bin, while raising the price by 50% ($400 to $600). Actually the closest replacement for the 580 is the 790, and that one costs a whole 75% more!
But the part that made me the least happy is their very small HEPA filters that are expensive to replace and that you are forced to use. I curse the marketing person who added this "feature" that forces you to give more and more money to irobot after already having paid 50% more for a robot that comes with less than the 580 used to. Paying for those expensive filters might make sense if you need them, but really blows if you're forced to buy them and don't need them.
It probably cleans a bit better, but to someone looking for a roomba, I'd recommend finding a much cheaper 5xx series or consider a Neato XV-21 which has real suction and room mapping (that one is however louder).
If you get stuck with a 700 series roomba series, I recommend buying filters from china via aliexpress, like 10 filters for $18 from aliexpress.