These machines are old school, require proper training and safety precautions, and are designed for specialty coffee shops who want to market themselves as an artisan coffeehouse or roasters! The benefits include the art of preparation in front of your customer paying top dollar for your service and beverage as well as highly desirable flavor profiles that cannot be duplicated on other types of machines.
Since there is no pump, these machines typically have better track records for repair and service when compared to other types of machines. The downsides are a) these are not high production machines, b) can have safety issues in regards to the lever coming up and hitting someone's chin or eye socket, c) lots of training for newer employees not experienced with these machines, and d) require some muscle to bring the lever down against the piston spring (in other words, not a good machine for Aunt Nellie!)
Operation: The large manual lever, on top of the grouphead, is pulled down and then slightly lifted to allow the piston spring to push up the lever to extract the espresso. These are not the levers that are found on the side of the grouphead, that when lifted, activate a microswitch which turns on a pump.