Las Condes is the largest city (comuna) of the Santiago region (and it was even larger when it was created, encompassing until the 40s the cities of Vitacura and Lo Barnechea). The city is safe overall. The main problem (like in all upper-class cities) is more robbery (house or car) rather than physical aggressions.
As the city is very big, it would be useless to do a general description. Click on each neighborhood below to have a look at the main areas where expats live: