TFA says this is optional, but it's a good default. The general case for most loan words is that even native Japanese speakers will find the English spelling much more familiar than romanization. E.g. in any Japanese shop you'll see signs that say "sale" or "bargain", but you'd never see "se-ru" or "bāgen" -- writing that way looks as strange to JP speakers as to anyone else.

"Cutlet" strikes me as an edge case, considering that "katsu" has more or less become a word in its own right. So, perhaps an unfortunate choice of name for this project...