I live here
San Martin is a big district, but if you are like me and go for a safe and family frienly area you will look for the limit with Downtown Lima. I won't encorage you to live here, because this district is not so nice to look at, it is not precisely beautiful. I live here for a number of reasons out of my hands, in a couple mothns I'll be ready to move for a more green district.
We have all services here as well, Malls, supermarkets, transport, you name it... And yes, I have to mention the airport is so close you can go simply walking... That is a pro!
The bad thing is the distance to the sea, and sadly the unconscious people who throw any kind of crap to the floor, I mean, the city clean all day long, but there are A LOT of people who simply wont use a trash bin and prefer use the floor for that purpose...