Having been to a lot of Grill'd restaurants both in NSW and interstates, I have come to recognise that those that are equipped with restrooms are usually the ones which restrooms you would want to avoid.
Grill'd Darlinghurst is one of them. Actually, it seems to me that their restroom is one of the worst restrooms I have ever seen in a long time. In the restroom, I witnessed brown smears over the wall, right above the mens urinals that is already very unkempt, judging by the sediments it has collected.
That is probably the only thing you should avoid when visiting this restaurant. Otherwise, you should be able to enjoy the intimate atmosphere of this small-scaled shop, complete with its free Wi-Fi -- something that is quite unheard of for Grill'd.
The staffs were friendly and prompt. I am pretty sure they are not in charge of cleaning the restrooms.