It's a hybrid or dual valve... they're pretty hard to screw up. I'd just build my own... oh wait. :P (see the link below)
I recommend against running it in the engine bay. Boost controllers should not be installed in any way that adds significantly to the volume of the signal line (10 feet of extra vacuum hose causes a lag in responsiveness and provides a LOT of area for a leak). Install it under the hood, tune it for the desired boost, mark it and if you want a second stage tune for that and mark it. I've seen some people make in cabin controls using aircraft cable and a worm gear type setup on top of the boost controller... You can also setup a dual pressure system using the type of blow off valve you show with a little modification and a spare 12v vacuum solenoid.
http://www.gusmahon.org/html/boostcontrol.htm The third one explains how this type works.