We loved staying at Zak's. It is exactly as advertised and Zak was very helpful organising an airport pickup and getting us settled in and was just a phone call away for any questions. There can be a bit of noise from the street but if you keep the doors to the bathroom and the closed balcony closed and the blinds drawn at night you should be fine. I didn't have any trouble sleeping. Aircon was good as
It was quite hot and having Netflix when we had quiet night in one night was also great!
The location is perfect. A few blocks down the road is the ferry to Sliema - if you want groceries I suggest you go to Sliema as that is where the supermarkets are. There are small shops on the Valleta side for basics. It's just a free blocks from the Main Street, shops and bus terminal. We spent a lot of time just walking around and soaking up the unique historical charm of Valletta.
If you turn right from the ferry there is an old (unused) public pool but just past that there is a lovely little rock beach used by the locals to swim - 5 minutes from the flat - and the water is beautiful
Recommend the yellow tourist bus to get round the island - less busy than the red one. Head to the other side of Valletta for a drink on a street looking down to the harbour.