The compressor Performance Products rents is made by Sir Products and is a virtual copy of the Klaan compressor in form and use. As for not using a compressor, I have heard all kinds of methods used, but none guarantees that a small slip of a supporting jack or whatever will not result in the spring popping loose, perhaps causing damage to the car or to the worker. On the old 108, 109, 110, 111, 113 cars M-B had a method using a jack and a tool that engaged the lower control arm pivot (and the trailing arm pivot in the rear). It was dicey at best in the front. At the rear it was much more secure because of the other locating methods incorporated in the suspension design.