Hi there. Saxophone player here. Started with Clarinet as a 7 year old, went to Sax when I was 10. Played em all...Alto, Tenor, Soprano, Baritone. I wanted to give you my 2 cents on what you should get your kid. I even used to work at a music store, so I've played a ton of these instruments.
I haven't played a Jupiter in a while, but at the time I remember being impressed for the quality of the horn at the price. If you want a beginner instrument that has comparable sound (it will always be different) to a Yamaha, which I imagine is more expensive, it's pretty decent. I was never a fan of the beginner Selmer's, at least the newer ones.
The bigger picture question is how much your kid wants to play, what type of Sax music he wants to play, and what kind of sound he wants out of the horn. Yamaha tends to have a brighter sound. I actually have 2 Yamaha Intermediate horns, and I used them for marching bands, pep bands, concert music...things like that. It just has a really good sound, and they are well constructed. Hard to go wrong. But if I was playing professionally chances are I wouldn't be using a Yamaha.
If your child is getting very serious about the sax, and you want this horn to be something he plays for 20 years, and he wants to do things like jazz, and you are willing to make the investment, and older Selmer Mark 6 is a GREAT saxophone. I have played many of them, and they are terrific. But an instrument like this is like a baby practically. You would actually not want a newer one, and it would need to be well taken care of. A saxophone like this is the type you never get rid of if you have one. There is something to be said for that when it comes to instruments. They are an investment and keep their value, but more importantly it's the type of possession you cherish the rest of your life. I love collecting video games, but there is definitely something different about an instrument. But I wouldn't go recommending right off the bat to just get one of these things...this would ONLY be if you think your kid wants to be a professional or make some other lifetime commitment to it. Otherwise, just get a quality starter horn. He can play that through high school and it will sound just fine. Don't go cheap on a beat up instrument. We found an old Conn that could have been good and tried to fix it up, and it never played right. Ended up just getting something different and it was a sunk cost. I think a rental is a bad idea based on what you say about your child.
All that said, there are a lot of decent horns out there, so if you are just looking for something for your kid to grow with there are plenty of fair choices. You can always upgrade later. Hope this helps.