I'd seen most of these before too (UK/Ireland), a butter curler is common and cheap. However the right angled curler is new to me; it seems to be a consequence

I'd seen most of these before too (UK/Ireland), a butter curler is common and cheap. However the right angled curler is new to me; it seems to be a consequence of their butter dishes being different tho? My butter dish (and most of the ones I've ever seen here) looks like: https://www.porzellantreff.de/en/Friesland-Ammerland-Blue-Butter-Dish-p32436.html https://www.porzellantreff.de/en/Friesland-Ammerland-Blue-Bu... (a flat plate with a cuboid lid), so straight butter knives with a curler edge can work right to the last of the butter, where the photos in the article show a cuboid dish with a flat top - the right-angled knife is going to be needed to reach the butter when the butter has been used to below the rim of the dish.