Frank's place has a very convenient location in Sliema and is ideal if you plan a short holiday in which you want to explore in all directions. It is close to shops, restaurants and a bus stop with direct connections to Valletta, Gozo ferry, Popeye Village, Mdina etc. The ferry to Valletta is also a short walk away. Sliema has a nice waterfront and is quieter than St Julian and (I suppose) more affordable than Valletta. But if you come for just a weekend, maybe stay in Valletta to save time.
The apartment is in a stone building with high ceilings, so I suppose it is ideal for keeping cool in summer. In winter, it gets damp and the AC is too noisy and not good enough to warm the main room (and not at all the bathroom and kitchen). If you are used to cooler temperatures this might not be a problem for you, but keep in mind there is no other heat source than the AC.
We found the place very clean and we appreciated there is a small kitchen with kettle (no coffee machine), toaster and oven (haven't tried, but it's good that it's there). However, there are still many improvements to be made (proper door at the bathroom instead of a fabric curtain, shelves/drawers for clothes, hooks for towels, fixtures in the bathroom, mirrors positioned at head level etc.). As it is, the level of comfort is low and the place is not ideal for longer stays (it also doesn't have a washing machine, dryer, proper table or desk, so not good for remote work).
Frank is very communicative, replies very fast to messages and tries to be as accommodating as possible. We appreciate he allowed us to check-in late and to store our luggage after we checked out, before leaving for the airport.