I have. I set it up on the other tv but the mighty couldn’t find it and I couldn’t activate it with the code from the mighty so had to start a new account. I wanted to be able to watch shows recorded on the Mighty on the Mini but because they are on different accounts I can’t
Recorded shows between the units may also be a no go.
Essentially RSP provided Fetch units are locked down. You never own them and they don't talk well with other units not from the same RSP. Its a business model.
If you don't care about a free Fetch Package from Optus then perhaps grab a refurbished mighty from the official Fetch eBay site. You own it and it can talk to other such boxes.