HI - Helsinki - Hostel Academica seems to be a student residence that converts to a hostel. Considering its price, it should (and does) offer more quality than regular hostels.
The location is not really central, but it's close to a tram and a metro stations, although in a quiet street. The directions given by the hostel's website are clear.
Rooms and Bathrooms
The rooms are comfortable, the matresses and the linen are in good state, there are wardrobes for storing things, and since no room is for more than three people, you can feel safe storing your things in them. All the rooms have equipment for cooking, such as an oven and a fridge, so you can save some money cooking yourself instead of eating in the expensive restaurants of Helsinki. Also, each room has its own bathroom, and there's space for placing shampoo and soap, clothes, and towels. The cleanliness of the place is good, and it'll be cleaned again in case you stay four or more days.
Given that all the facilities you could need are in the room, you won't see people very often. There's a common room in the ground floor with TV, some books, and tables for seating and talking, but you won't see so many people around there. Wi-Fi is available only in this room, but it's not provided for free, so people don't have many reasons to go there. It's more of a high-level hostel, so you'll see older people and mature couples. It will be quiet most of the time, but there are pubs right in front of the entrance and in the same block, so there are other options.
The service is better than you'd expect from a hostel, so if you want to spend a little more for better accommodation, this place is recommended.