OEM, as in Original Equipment Manufacturer stands for companies who make the original parts for car factories. These pars are the same or exceeding quality as the original parts on the car. These parts are thus suitable for everyday driving and trackdays.
Install kits make your life a lot easier, as instead of working with rusted and worn clips and spring you can use all new hardware which wont jam or stick. Servicing calipers imporves brake feel a lot.