I tried a Bumbo with my third baby, and we haven't gotten much use out of it. A friend gave me hers to use and I bought a tray for $10, so I haven't spent too much money on it, luckily.
My son sat at an early age also (he's now 7 1/2 months old). Whenever I sat him in the Bumbo, he would bend all the way over to the floor or arch his back and has actually flipped out of it! He stays in there a little better with the tray though. He'll still sit in it for a short amount of time, but he's crawling too, so he doesn't like to be stationary for very long.
My advice is to skip it. It's a great concept, but if you have a Boppy pillow (or any other kind of pillows), you can help them practice sitting up safely. If you already have a bouncy seat, stick with that - they can be used earlier on and for a longer time. My kids have always enjoyed the swing and the exersaucers too!!!
BTW: I'm a mom of three boys! I was desperately hoping for a girl this last time, but I wouldn't change it for the world!! Good luck with your little blessing - whatever the sex may be! :)