For your baby to be ready developmentally for a toy like this, he or she definitely needs to be able to hold his head up and be able to sit up fairly well. I think the recommended age is about 6 months, but we put our son in the saucer at about 4 months because he was strong and we felt he was ready for it. We waited a little longer for the jumper, since it could jostle him around.
As for brands, we had the "Intellitainer" by Fisher Price, but evidently it does not exist anymore. It was a gift and at first, I just thought it was ugly and enormous but once we put it to use it was GREAT. It had a seat that slid back and forth on a track within the toy so our son could move around and play with all the features. It had electric lights, music and sounds, as well as a "book" and quiet toys. And he loved to pull himself up on it and continue playing even when he outgrew the seat. The pros are the number and variety of activities it features - way more than the Baby Einstein saucer. The cons are its size (bigger than most saucers) and that it doesn't fold away. I was always kind of jealous of the saucers that collapse and can travel with your. But, we just recently put the Intellitainer away and our boy's almost a year and a half. It was a lifesaver!
We also had a Jumperoo and although our son liked it, I don't feel like he loved it enough to justify the size of it and the price - I think it was about $60. It is huge and even though it "folds away", it's not really a space-saver. And the music is really annoying. Aside from jumping, there's not much for the baby to do with it. But to let you know, our son never walked on his toes so we don't have proof of a correlation there.
For either of these toys, I recommend borrowing one from a friend or picking one up at a consignment shop before you commit to a big purchase. They can be great toys, but they can also be great wastes of money if your baby isn't into it.