Supermunchkin Thief, so no downsides. Free stealing?

[kintrix]

One of us was a Supermunchkin Thief without a secondary class, so they do not have the downsides of a Thief. To me this obviously means that they can use items Thieves cannot.

However, they insisted this means that they do not lose a level if they fail a steal, because that is also a downside.

We are playing the game in Hungarian, so I cannot quote the cards, but in case the card initially says "no downsides of BEING of that class", then this is solved. No free stealing.

I'm curious whether this is OP, or it does, indeed, only allow you to use items you normally couldn't?