This is technically a correct Welsh word, but please don't ever use it unless you want funny looks. Go for beiro or pen!
I did wonder why I had never heard this word when doing Welsh at school!
Funny story : my friend from Wales was visiting me in the US and asked for a beiro. I looked at her with the blankest look. It led to a conversation as to why it was called that. I had never heard the word before.
Yeah in Australia "biro" is kinda a retro word from the 80s ... most people probably know what it is, but it's just easier to say pen