I wouldn't be without my Roomba, in fact I bought a secondhand one on Gumtree so I have one upstairs and one downstairs.
When buying the first one, like you, I thought they were expensive so bought one of the generic (cheaper) ones and that was a disaster. The first one lasted approx 30 mins before it died, the second lasted 15 mins and then the seller problems started. Thank goodness I had bought it on eBay as I had to open a dispute to get my refund. So after that experience I only recommend iRobot Roomba, rather than cheaper generics and have NO affiliation with iRobot. LOL
I have a Dyson rechargeable handheld for the stairs but the Roomba does everything else including floor rugs, except the longer, shag pile floor rug but I do that with the Dyson and really it's not a big deal.
The corners and edges are done properly because there is a rotating brush which extends past the side of the Roomba and this reaches into corners and along edges.
Because I'm retired I bought the less expensive model (531) which doesn't have programming, so I have to press 'clean' when I want the floors done...again, no big deal!
If you have pets, then a pet-model is recommended, I have friends with both cats and dogs who live in the house and they highly recommend the pet model.
Floors upstairs are carpet and downstairs polished porcelain tiles with rugs, I have since bought an iRobot Mop to do the tiles and that is great too. I just wish I had known about robot vacs when I had back surgery, as my floors weren't done for 12 weeks!
Hope this helps? good luck with your back.