I stayed at the HGI Mongkok during the third week of february and I can only conferm the recent good reviews.
I booked a cheap rate of 640 HK$ per night and I got an upgrade to a nice city view corner room at the 17th floor. Being at the end of the corridor the room was slightly larger than a regular room, with ample space for the bags at the entrance.
Breakfast good, with some made to order options. Position is OK, within 5 minutes walk from both Mongkok or Yu Ma Tei MTR stations (probably the second being closer to the hotel).
Usually rates are below 1000 HK$, expecially because the hotel is very close to the Holiday Inn Express recently opened. But with the rate of 640 HK$ I paid this would be my first choice when in Kowloon.