We stayed for 4 nights at Ah Shan hostel, and were pleasantly surprised by the quality of this hostel. Being away from the main hostels scene in the Chungking Mansions is a really good plus. You are located in Mong Kok, a perfect location to get into the pulse of Hong Kong and explore all the faboulos cuisine by trying out locals restaurants.
The room was small, but clean, the shared bathroom was quite of a challenge though as the shower did not have a door so water spilled all over the place. The sink is also quite small but you may get used to it.
The staff is fiendly and helpful. The hostel also propose discounted tickets to some major attractions, make sure to have a look.
Overall I would recommend the hostel if you are in a tight budget or just need a place to crash at night while exploring the city.More