Karl's flat is very well placed and very well located if you want to walk around Malta. The pool is heated and this allowed us to take some time out after a busy day.
The flat has all the facilities you need. The only downside is that other flats are rented in the building, in our case we were there during a festival period so there was quite a bit of noise from the other flats.
Plan to rent a car as it is easier to get around the island. I highly recommend this flat if you want to go to Malta.