As much as I appreciate the restaurateur intentions let's see it for what it is: marketing gimmick. 

Like kosher, you can't have a halal meal in a haram venue. It's a whole process, set of rules, not just the ingredients.

Some customers, who like to keep appearances, but are not really observant might go for it. Maybe some curious non-muslims, but that's it.

And one more thing: halal meat is more expensive. Selling it a at the same price with regular beef means customers pay more for non-halal beef. Probably not much more considering the few halal orders.