I did not have a Bumbo with my first little guy. My doctor recommended I get one to help my youngest build up his core strength. Max was behind being able to sit up on his own or even attempting to do so. This seat stays flat on whatever surface he's on and I do not have to worry about him getting hurt. So, it keeps him from falling over and gives him some support, but also some flexibility so he has to lift himself up if he bends over or leans back, and thus develops those important abdominal muscles.
This particular Bumbo also comes with a tray that can snap in allowing me to feed him in a secure seat, and makes it a little easier and gives me a little freedom since he's not on my lap. I can also loop a toy with a ring onto the central seat strap so he can't drop it. Keeping him entertained for a few minutes helps, when I'm getting his food together. The tray slides and snaps easily onto the back of the chair for easy storage when I get him in and out of the chair.
Max is a big baby, around 20 lbs at 6 months. So, it fits big babies with the green cushy foam seat on. I removed the green cushion today so he can have more leg room. He's 9 months and sitting up on his own now, and still has plenty of room to grow in the seat. I also like having this seat, because I can have him in the Bumbo, and my oldest in his high chair, and we can all eat at the same time.
The Bumbo is also easy to take apart and put back together should you have a poo explosion on your hands, as I found out. I did not need to consult a manual to take it apart, or put it back together, which is appreciated. So, if you are looking for a booster seat for your little one that is transitioning to sitting up, I recommend this one.