I feel that is a little too expensive for 11 years old Sax. I have recently got a Tenor and Started playing it a few weeks ago after 3 or so years on the Bb clarinet. The USA Selmer 1244 seems to have a really vibrant and nice tone to it. But I really can't say how much since mine is used and got it for 450.00 as mine is a bit older than 11 years and used. I would say having a new good condition Selmer USA is good but 1299.00 is a bit pricey for me. I would recomend to try and get the price down a little. but I have a suggestion, although Selmer USA is a good brand and I REALLy recommend it for your son and everyone.  But if your son would want to carry on sax in the future and want to have a more professional level one, I would Keep your head out for Selmer Paris. Which are  better brand of Saxes and are Pro. As I said before though, Selmer USA 1244 is a great brand for your son, and it has really good tone quality and pitch. I couldnt compliment it more!! Just try to bring down the price if you can and you can get a really good deal for it! I hope everything works out qith you and your son!! :)
With regards,
Aisaka