My wife and I spent 6 nights at Charlie's flat, and we higly recommend staying there.
The flat is on a very quiet street (very little traffic) about 2.5 kilometers from Mdina with bus stops and a small grocer just around the corner. Also, the flat has a wonderful rooftop terrace with excellent views. It's just a short walk to St Paul's Catacombs etc.
Be aware that Maltese houses are built to keep the summer heat out, which means that they can be a bit cold between late fall and early spring. Charlie's flat has got A/C heating in the rooms and an electric fire in the kitchen, but the corridor is a bit chilly - so bring indoor shooes and a woollen jumper.
If you feel like a chat, do talk to Carmel (Charlie). He's easy going and very knowledgeable about Malta. From his own extensive travelling experience, he knows what travellers need when they are abroad.
We will certainly try to stay at Charlie's flat next time we are in Malta.