If you use weasel piss gas the system will only let you run so much boost.
89 would probably only give me a max of 10 psi on a cool wet day. The Saab system backs off boost when it senses knock while the Volvo system backs off timing. At 14 psi and 89 octane there isn't enough timing to back off to stop the detonation in 95 degree heat under load. Those other after market boost enhancers have no way to back off the boost if it the engine starts knocking. If the nut at the wheel has his stereo up at 120 decibels he or she will never hear it until either a rod finds it's way through the side of the block or a hole the size of a half dollar appears in the top of a piston. The APC piggy- backs the Volvo system so if it ever failed the Turbo would revert to the factory set 7.5 psi.