Someone shared the Rootstock project with me, which aims to bring smart contracting functionality to Bitcoin. I am after some technical opinions and overviews of what it is and what it does please.

I was surprised to learn that Braiins Pools and others are already performing merged mining of Rootstock as it can reuse the hash rate.

How does Rootstock fit into the Bitcoin ecosystem? It has been around for a while but I see little discussion of it here. The peg-in and peg-out happens on Bitcoin, but where is the smart contract code actually executed?

There has been a lot of criticisms of BIP300/301 drivechains, but what is the difference between that and the projects / sidechains such as Rootstock, Liquid, RGB etc?

Thank you.