I stayed here in June for one night in single sex room (floors were mixed, fyi) and found the location to be fine for exploring the city. It was easy to find and walking distance to the bus station (a bit tiring carrying heavy luggage though).
The hostel was great about communication prior to arrival via email (you can find a general hostel website for Croatia and Zagreb is one of the hostels listed). They also sent a map and that was handy to have ahead of time.
All the travellers I met there were friendly, the proprietors didn't seem very social. There wasn't much to do at the hostel that I found: just a "break room" and a soda/snack machine. You probably won't want to hang out at the hostel, it's just a cheap place to sleep and then leave.
Showers and toilets worked fine but considering we were taking cold showers to survive the room heat, not sure how the hot water in winter or fall might be. Or heating in general, for that matter.
Biggest complaints: in summer the very small room was stifling hot and the window only opened part way (no ac). Also light coming in room at night and noise from outside.
One key for the whole room so it has to be passed from person to person and left at front desk by last person to go out. Not sure about luggage storage outside of the room, there was a wardrobe in the room and didn't encounter any problems, but there wasn't any "lock," either.
Compared to other hostels I've stayed at, this one was borderline. Not especially enjoyable. But bearable, and nothing horrible. There was a mix of people staying there, including groups of kids.
One important tip for the bus station if you're taking a bus to the airport: the location of the airport bus was NOT in the same area as the regular buses which will be lined up with people getting on and off. I didn't see any signs or info on the directory there and a guy at information just kept telling me it was near the taxis. (Yeah I was trying to ask in Croatian). However, that is NOT the taxi area where taxis are parked near the street with buses driving by and a bus stop. The airport bus will not drive by you. It will be parked in its own area, waiting for boarding. I missed the first airport bus because I kept standing in the wrong place watching buses go by and walking around trying to figure out where I should be.
Luckily, after getting no clarification a second time from "information," a lady at the kiosk pointed me in the direction of the airport bus area, which was up out of and around the side from the normal bus area. (One minute from where I was but not viewable from regular area.. I think there was a chain link fence and maybe a few steps to go down). Depending on what side of the station you come in on, you may not see this area. I was there at 6am and I hadn't arrived via that station so I was clueless. If you have any problems, you just walk out from where the normal buses are parked, and walk to the side (to the right of the Kiosk area at that time), then you should find it.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC