What is sirloin tip?

I'm completely on board with my pal ChefOno's answer. The sirloin and the round are indeed two different primal cuts. The round being closest to the cow's butt. This is going to be tough meat to chew without someother massaging. There was an interesting article in the Wall Street Journal (of all places) recently on the wacky names that food purveyors are coming up with to make certain cuts more interesting or palatable. Of course this practice has been going on for a long time and I could start with seafood...

Officially, the sirloin tip is a cut from the round. Since the sirloin and the round are two different primals, right there you should be able to detect some degree of... let's call it "marketing". There are numerous synonyms including what it should be called, a round tip. But stores will also package other cuts and label them sirloin tips. It's not a cut I specify or purchase for those and other reasons.

Also, some people refer to flap meat as sirloin tips (and the other way around).

In other words, I can't answer your question. I'd grind it with something fatty or braise it.