So I've sat both the MMI and most recently the CBI. My experience of both was extremely positive - they were nothing but helpful and I got the feeling they wanted us to succeed. In both interviews, they promoted me where necessary and probed where they needed certain info.
My advice for the MMI is to make sure you supply detail, detail and more detail! During my CBI I wasn't promoted that often for more info as I had gone into enough depth already. I guess just make sure your answers are relevant and focus only on what you did! Not others. My examples were fairly simple but met the criteria - i didn't want to bog them down with complicated sceneiroes!
