ISOFIX mounting points are intended to make the child seat easier to fit, because the seat doesnt use the seatbelt to keep it in place. The system was originally introduced so that all cars would accept all child seats, but this hasnt happened. Not all ISOFIX seats are compatible with all cars, so check with the car manufacturer or seat retailer before you buy.
Many ISOFIX seats also require a third anchor point either a leg between the base of the child seat and the floor, or a top tether over the back of the seat to an anchor point in the boot which complicates fitting. So, in reality, ISOFIX isnt necessarily a simpler option.