Firefighter, despite a few misconceptions posted, Pacbrake has many options to suit your current needs and if you have future modifications planned we can advise you on your best retarder options. Direct mount brakes like our 4" Max-flow elbow are the preferred choice for many reasons, although as someone pointed out already that if you change your turbocharger for more HP later, a direct mount exhaust brake most likely won't fit. This statement is correct, therefore an inline mounted exhaust brake would be the correct choice if a turbo upgrade is planned for future HP gains.
Pacbrake's performance exhaust brake "PRXB" is a mechanical way of holding the engines maximum allowable back-pressure to low RPM, another manufacturers way of doing it is electrical, cycling the exhaust brake off and on rapidly as a means of regulation. The electrical cycling method relies on a pressure switch in the exhaust system which when it plugs up with soot will overpressure the engine.
Pacbrake kits for automatic transmission vehicles includes a torque converter lock-up controller, if you want to save money you could purchase a kit for a manual transmission vehicle and do the mystery switch torque converter lock-up as some customers do, although doing it that way requires more driver interaction.
The Pacbrake PRXB system uses an air compressor to apply the exhaust brake, with this system you get on board air which can be used to operate accessories like an air horn, fill air springs or top up a tire. As for the comment on the location of the air compressor it is NOT mounted on the engine on 2nd gen trucks.
The subscribers to this site are extremely knowledgeable and passionate about their trucks and choice of accessories. My advise is to read and listen to what they have to say, then make a list of questions you feel are important to you and your needs. Then call the manufacturers of the product you are considering to ask the questions that are important to you. I'm sure the choice of who's exhaust brake to install will become clear.