Raven is PDI.
It's their "lower end" brand. Cheaper, all plastic piston. Aluminum cylinder (vs. steel). The piston and head has an integral airbrake and the piston is VC type.
Overall it's good for the price for sub-450 rifles (there is no point in going higher anyways...)
http://www.x-fire.org/m24/raven_cy_f...cyfullset.html