Just had to express my opinion here. I think pure Yorkies and pure Biewers are all beautiful. I would like to have a Biewer myself, but have a new Yorkie pup already, and don't want to pay the price for a Biewer.
Personally, if I was looking for another furbaby and a Yorkie/Biewer mix came available at a good price and I did not intend to breed but have as a pet only, I'd JUMP at the chance.
Go for it!!!
You may have a really unique pet, and if it does default to look like a Yorkie, depending on the quality of the Yorkie parent, you may have a high quality baby at a reasonable price.
Wish you the very best!!!!!!