When I had my second child, I had no intention of getting anything like this... my first had been content with his rocker, so I expected to use the same again! However, I soon found myself with a child who, by 3 months, was miserable lying down while awake. After spending almost all his waking hours holding him in a sitting position, I went looking for something to give me - and his somewhat sidelined big brother - a little respite.
I looked at a bumbo, but it was clear that my chunky baby wouldn't fit in one for long. This was recommended to me as suitable for larger babies and as the price was comparable, we went with it.
Best thing EVER! It arrived quickly and was easy to assemble. It's really only a matter of screwing the bits of the tray together and clicking the toys into place. My boy loved it and the difference in him was noticeable - he stopped crying whenever you put him down and that made me happier too! My oldest was also impressed, as he could now interact with his little brother!
He's happy to sit in it for 10-15 minutes, pretty good for a baby. It also seems to have helped him learn to sit on his own - he's not quite 5 months and already sitting unsupported for a few minutes at a time. I am sure this is partly because of the seat!
If it has any downsides I'd say it's not quite as portable as a bumbo - I can't put it in the bathroom while I shower because it's just too big and for travelling a bumbo is far less likely to get damaged. But those are really minor things - this is a fantastic product that has saved my sanity!