Actually, I disagree on this one. I'd like the minion myself but it's not important in any way to have, which makes it perfect as a super rare item. Having items that are super rare makes them all the more exciting to see, and if you're doing repeat dungeons it's good to have that little feeling of "just maybe".

Having the item tradable is also good, because it allows people who are desperate to just obtain it through gil if they want (also some people don't enjoy dungeons much but may like to craft and make a lot of gil). If you already have the oppo, you would not be saying I wish it wasn't tradable when a second drops ;P There's no harm in this in my view. I'm always short on gil and I like that there's a chance I'll possibly grab a super expensive item sometime and make a fortune on the market. More rare minions please.