Overall, as a 20-something, using this as a cheap place to sleep for the night while seeing London this worked for me and allowed me to spend my travel money on the things I wanted to do. The hostel does provide breakfast, and a 10% off discount for anything you order at the bar (burger and a beer is normally 15 pounds, so you get that for 13.50). The staff was friendly, and the bedding was clean in the hostel. The showers had warm water and seemed to be cleaned on a somewhat regular basis. The bar area is open to you 24 hours a day, though the kitchen closes at 10 and the bar closes to the public at midnight.
Beyond that, you can't beat the location in terms of it being a launching point for getting around the city. You are on several bus lines and three different tube lines. You are also only a mile's walk from Hyde park on a main road that is well lit, even at night.
First off, if you are a light sleeper, don't choose this hostel. It is on a highly-used road and the windows will be open in the room. If you wake up at every horn or siren, you will not have a good time sleeping here. In addition to that, the larger rooms have 24 people, so you can expect them to be coming and going at all hours, some quietly, some not (which also means your experience is not 100% on the hostel staff). Bar noise was non-existent, so don't worry about that.
The breakfast was a bit of a zoo, and a bit of a disappointment. They had loaves of bread with a toaster (butter and jam), some cereal and milk. There was also tea and coffee. It was pretty well picked over by 8:15, and the staff was too busy cleaning the bar to replace anything. To that end, the staff in the hostel always seemed to be stretched too thin. People are working the hostel front desk and the bar at the same time. They are not mean about it, but if you catch it wrong, you can end up waiting a bit to be helped. There were also a few people who were sleeping in the hallway at times, though I was not sure if they were just too drunk to remember their passcodes or had snuck in. Also, I never saw any semblance of a manager for either the bar or the hostel (not that I ever needed one).
The cleanliness of the rooms and the bathrooms left something to be desired, the rooms especially. Though I didn't spend much time in them, there was usually some crumbs / scraps of wrappers on the floor, which did not feel clean even when those larger pieces of rubbish were not there. This comes back to you experience being tied to the people you are in the room with however. In particular, there was one person who's luggage smelled like a college student's laundry bin that had been left to sit during the winter break, in-short, really bad.
My final warning would be that there are not a lot of power outlets in the rooms, and there are only two bathrooms to accommodate 50+ people, as opposed to 4 showers.
