I have a similar one for my son. Paid £20 for it used as he's 7, a beginner, growing and doesn't ride regularly. They are fine for that sort of thing but for anyone who has stopped growing and/or who ride reguarly, save up your money and get a decent saddle.
I see this is qute an old post, please do not use this saddle , if you have continued to. Just because your son is lightweight does not mean that if the horse were to buck or spook suddenly that the webs may not break due to sudden increase in pressure. If budget is an isssue find a second hand modern synthetic, please!