If you read on poolforum you will find main drains are a big source of problems. They make sense as they will keep the pool cleaner with less effort but they are on the bottom at the deep end and no way to get to the pipes or assembly easily and cheaply. I would never have one. If or when I get another pool and have a say in the design, I would provide a water level suction port and rig up something on a flexible hose that I could sink in the deep end and perform the same function as a main drain. Could be easily removed when the pool is occupied. My pool has an 8' deep end and most of the crud settles there and it's no big deal to take a few minutes to vacuum manually.
Al