I broke DS tablet wwyd?

Do not replace it, you have seen with your eyes how much his behaviour deteriorates when he uses the tablet. Let him choose a toy or something for a hobby and pay for it. Explain to him that he is not mature enough to have a tablet. Tell your in laws what the replacement is and make sure they know they have not to buy him any tech without your say so.
Yes you need to apologise for throwing it and you need to explain why your behaviour was wrong. For all those who are outraged by your behaviour, just know if their child had painted himself, the kitchen and the fence they would not be saying "oh dear Johnny, what a silly billy you have been" They would be having a hissy fit too.

Long story short, you didn't parent him effectively and so you're justifying flying off the handle.

You do know that abusive people can always justify it? They were always "pushed to it".

👆This
All you have done is shown him you are the households 'smasher in residence'. You need to address this.

Pretty poor parenting OP.

So why didn't you just tell him that it had been put away?

ok you should have smashed it, but I understand the frustration they can cause

I would tell your inlaws the issues he has been having using the tablet, it’s now no longer around and won’t be replaced but you will put the cost of it into his bank account

i would also advise them they are not to get another one, or indeed any electronics devices without running it past you first

No, don't replace it. I missed how old the child is but he sounds too young and immature for a tablet.
You also need to make it clear to the GP that they cannot ruby him another one and that he will be screen free for the foreseeable future.
You do need to work on your anger management though. Smashing things up is not right and sets him a poor example that this is what we do when we get angry.

I think you need to put the money into his account at the very least. Amd you need to get your dh to tell husband parents that electronic devices like that need to be discussed with you both beforehand.

There is a huge line between acting as a parent by responsibly monitoring your son’s use of his iPad -
to smashing it up so that he can’t use it at all.
You might think your son isn’t aware of your family/emotional issues but he will absolutely be aware of your behaviour and perhaps copy what he sees.
You need to reassess your parenting style and stop blaming your poor choices on your son acting out.
Yes it is hard work monitoring iPad time but that’s your job - it’s called parenting.
Kids don’t magically learn how to regulate themselves without guidance.

I think you should explain the impact of the tablet on your family. Admit that you were wrong to have smashed rather than returning it to them. Make it clear to them that he is not to be given any technology related gifts in the future nor is he to have access to them in their house.

Do nothing. Tablet is gone. GP don’t need an apology for a toy that caused so much trouble. Just keep actively parenting your kid and keep him away from screens as much as possible

I can really believe that bad behaviour was caused by a tablet. My grandchildren are changed children since their tablets were removed from them.
OP, I think the GPs should have asked of it was OK to buy them tablets before they bought them.

Give the grandparents money for a new one and say the rules are he can only play with it at their house.

I don't see why you should give the grandparents anything - it was gifted to your son - why would they get the money back? I can understand them being upset and I'd have a conversation with them acknowledging that you were in the wrong for smashing it and acknowledge their frustration. Whether you replace it is up to you - if it's causing that big of an issue with your son then you certainly don't have to. Perhaps you could buy him something else to play with - open ended toys like connex tiles could be a good idea.
And please be kind to yourself - You're only human and everyone loses their shit sometimes. Perhaps use this opportunity to reflect on what was building up and how you can find healthy outlets so that you don't blow.

Confess to your DS and apologise.
Explain to the GPs and offer to refund or buy a replacement gift. If they give another tablet, confiscate and return it.
Ideally, they/you should put the cost of the tablet in a savings account/shares ISA. It will do your DS more good in the long run.

“They said to ds I need to apologise and replace it but we won’t be doing that. Should I just give them the money?”

I know imagine you apologise to your child because you were a shit parent. Poor kid

If you had taken the tablet away, this wouldn’t be a problem.

its the smashing the tablet that must be rectified. You need to show your child that behavior is unacceptable. How? I have no idea.

Also if he is too young for a tablet how has he got access to garden paint in order to do that much damage whilst you pop to the toilet

How old is he? I can't believe that it is just the tablet that is causing this change in his behaviour. Many children have tablets and don't behave this way.
Did you monitor what he was looking at on the tablet? Restrict access etc? No child should have unrestricted access to the internet.
Breaking the tablet was a very extreme reaction and I can understand why his grandparents who paid a lot of money for it are upset.

Obviously you shouldn’t have smashed it. But obviously you shouldn’t replace it either!

I would return the money to them or buy a replacement gift. See which they’d prefer.

Make it clear that he’s not to have tablets or similar tech because it’s harmful to him.

How old is your child? Yes too much screen time can cause problems but I don't think many children change overnight from well behaved to outrageous behaviour or the other way around. I would think there is something else going on

The tablet seems to be the least of your worries OP.

Blaming your addict brother for your poor, impulsive and childish behaviour is probably quite typical behaviour from you.

I can't believe you smashed up his stuff because he smashed up your stuff.

You do know you're supposed to act better than your 10 year old don't you?