I had the perfect experience for my first time in a hostel! The place is very colorful, clean and welcoming and the staff is so great. I met a lot of nice people. The helper of the moment, luciano, organized nice day trips around to allow us to see the most hidden and beautiful places. I recommend highly!
Concerning the surroundings, yes it was noisy during the night but I just listened to music when I wanted to sleep. I didnt feel it was a dangerous neighbourhood, because there were policemen keeping an eye on the piazza. I have been warned about pickpocket and I've been very careful with my stuff, nothing happened.
My last advice would to not be afraid of Napoli and its people, because once you get to know this city, you fall in love!