Nope, there's no other symptoms, Janey. Just the bad breath.
However, she often gets ear infections which the ENT has recently said are caused by the tonsil stones.
DD will often complain of having a 'yucky' taste in her mouth, being able to feel something at the back of her throat, and will sometimes lose her appetite when she gets a particularly large one which has built up.
But really, this past year, she's not been complaining as much. I think she's just got used to it.
The smell is the main 'give away' symptom though. When she has a large one, the smell is so bad you can smell it as soon as you walk into her bedroom in the mornings.
Definitely don't be put off going to the GP. Best your son hears you talking about his bad breath rather than other children talking about it in front of him at school.
I've actually started my own thread about dd's tonsil stones. The GP was very dismissive of them and said that bad breath wasn't enough reason to get her tonsils out. He clearly didn't understand how bad the smell was, and how it impacted my dd.
Thankfully the ENT has taken a more sensible apporach and has put her on the waiting list for an op.
If the smell is really bad in your son, you should be able to see the stone when you shine a torch in his mouth. However, it might be buried in one of the crypts in the tonsil, or behind a flap, so you may not see it.
They're horrible. And nothing gets rid of them except getting the tonsils out. No amount of gargling, changing diet etc will close over the holes in his tonsils, thus stopping bacteria/food building up inside them. Just in case the doctor says 'he'll grow out of it'.