Is there some check you can do to prevent installation on real hardware?

Considering that it's a bootcode, there's not really a way to install it "legitimately" anyways. Bootswap allows you to install any boot code you provide it (though it complains far more loudly about some than others), so it's not possible to outright prevent its installation. I suppose I could also add checksums for it to bootswap and have it inform you that this ROM specifically is known to brick physical calculators. However, I think it would just be sufficient to not provide the bootcode in a way that's convenient to install with bootswap, and put a warning above the download that the bootcode itself will brick your calc. If users want to try to install it anyways after that, that's their problem.