It's not unsafe, it's just buggy. They'll eventually put it back in the guide after they figure out what caused the bricks.
Well, the main dev of implementing a9lh wasn't able to replicate the bugs. She believes it's made of random chance or something alike. Although I haven't read anything in regards of her quitting the investigation on the topic. So let's wait and see.
It's unsafe if you can't figure out what's failing on you. And n3ds aren't cheap dirt like to be throwing them out the window.
Weren't OTPless bricks unfixable? I don't recall anything about those bricks getting fixed via hardmod (Since i guess most users lacked one before attempting) I remember something about the keys being tweaked and in a vulnerable state while bricking, but that's it.