This was a great place to stay while visiting Malta! I was here with my wife, brother-in law, and a friend, and there was plenty of space in the apartment for everyone to be comfortable. Having two bathrooms was especially welcome. The apartment was clean and the terrace was very nice to have for evening drinks or breakfast. Due to the weather, we didn't make much use of the rooftop terrace and pool, but under different circumstances we would have had a great time hanging out up there as well.
The hosts were very on top things, had excellent communication, and were extremely understanding about some changes of plans we had to make at the last minute. I'd give this place 5 stars just for how chill they were throughout the whole process.
In terms of location, it really depends on what you are looking for. Malta's attractions are spread out across the island so you will always be a bit far from something. Mellieha is well-situated for beaches, restaurants, bars, and the absolutely bizarre experience that is Popeye's village. There are a couple of stops for the airport bus (takes a little over an hour to get there) and transit is readily available to go to Valletta and other areas (also about an hour on the bus). I found most cab longer rides (Valletta, Mdina) were about 20 Euros. There are bakeries, grocery stores, pastry shops, ATMs, bus stops, and pretty much all of the basics you might need within a few minutes walk from the apartment.
I really don't have any significant complaints about this place. I guess some of the basics on offer were a bit light (no tea, coffee, body wash, shampoo), but that wasn't a sticking point for us as all of that stuff is easily available in the immediate area. Would highly recommend staying here!