Must have on a Cessna 340A... Spoilers--the ability to emulate the flight characteristics of a rock is a good thing when you're shooting approaches with jets and approach wants you down now. You can also use them to kill all that excess airspeed when you need to.

--Brian A Bros

"PowerPac Spoilers offer the opportunity to steepen descent profiles without thermal damage to power plants."

-- Private Pilot Magazine

"Until you've flown with PowerPac Spoilers you don't know what you're missing in terms of aircraft control and management of aircraft spacing."

-- Jack Brush

"We have yet to be faced with a questionable descent profile. It is with the utmost confidence that we begin our final descent from 16,000 feet ... just 20 miles from the airport. Your product has performed well … I recommend it to all Cessna owners."

-- Joseph A. Biasucci

"The ability to descend quickly through icing or turbulence was my primary reason for installing the PowerPac Spoilers and I am delighted with the results."

-- Gerald S. Fahringer

"We have the PowerPac Spoilers installed on two of our aircraft. The Spoilers are useful in getting down without circling and without reducing power and causing engine damage or losing pressurization in the cabin."

-- Jerry Sonnemaker

I ABSOLUTELY LOVE THESE SPOILERS. MY MAIN RATIONALIZATION FOR THE 'SPOILERS' WAS TWO-FOLD: 1) DECREASE FURTHER THE NUMBER OF ENGINE RPM CHANGES THAT I HAVE TO MAKE DURING A FLIGHT; 2) MINIMIZE THE "WEAR-AND-TEAR" ON THE LANDING GEAR (WHICH I HAD TO DROP IN ORDER TO AVOID EXCESSIVE AIRSPEED DURING A DESCENT. IF THESE SPOILERS ACCOMPLISH THIS, THEN I WILL BE VERY SATISFIED WITH THIS REASONABLE INVESTMENT.
HERE IS THE SUMMARY OF MY MAIN IMPRESSIONS:

1) THE "SPOILERS": GOD, THESE ARE WONDERFUL!!!!!!!!!! THEY WORK EXACTLY AS ADVERTISED. FROM A HIGH ALTITUDE (ABOVE 15,000 FEET), THEY ALLOW DESCENTS OF 1300 FEET/MIN AT 160 KNOTS WITH THE ENGINE SETTINGS UNCHANGED FROM CRUISE SETTINGS (32" MANIFOLD @ 2500 RPM). THE TRUE ADVANTAGE IS NOT HAVING TO DROP THE GEAR TO SLOW DOWN AND BEING ABLE TO LEAVE THE ENGINE SETTINGS UNCHANGED. DURING DESCENTS AT LOW ALTITUDE (BELOW 8,000 FEET), THE RATE IS ABOUT 1,000 FEET/MIN @ ABOUT 170 KNOTS AIRSPEED INDICATED.  THEY ARE ENTIRELY FLAT AGAINST THE WING WHEN NOT IN USE AND ARE INSTALLED ON THE OUTSIDE WING PORTION NEXT TO EACH ENGINE JUST FORWARD OF THE FLAPS. SURPRISINGLY, THE NOISE LEVEL WHEN ACTIVATED IS JUST A VERY LOW VOLUME RUMBLE. O' LORD THEY WORK WELL, THOUGH.

-- Frank

Cessna 337 Power Pac Spoilers...perhaps one of the best STC'd items available.  I come down from altitude at full cruise power and RPM...never having to "pull back an inch at a time" as you'd do in a normal twin...because, the spoilers bring me down at 1000 FPM without exceeding the Green Arc. 
 This is a perfectly engineered solution to avoid shock cooling the engines.
-- C-337 owner

PowerPac spoilers allow you to decend at rates in excess to 5000 feet per minute while maintaining cabin pressurization.  These spoilers are designed to limit the amount of pitch change and buffetting experienced.  They are hydraulicaly operated using the aircrafts hydraulic system and simply operated by a push-button switch.
--aerostar-aviation.com

I had the spoiler package installed on my 58P when I changed over to the Ram engines. I have found that yes if you are able to plan your decent and not cool the engines they are not needed. But in the real world this does not happen everytime. I am able to deploy the spoiler and flaps at 170 knts, reduce the power 2 inches and decend at 1500 to 1700 ft/per/ min. The engines stay hot and I have great control. I recommend that you fly a Baron with spoilers to see how they function.
---BeechTalk Forum

I have had the spoilers on my C414A Ram VII now for approximately one month. They are FANTASTIC! I can now easily comply with ATC's "expedite descent" requests without any workload stress or shock cooling of my engines or stressing the landing gear.  "Maintain altitude for crossing traffic" as you approach your destination is no longer a problem.  Fast approaches into large airports with busy jet traffic is much less stressful.  Additionally, I am able to make up time lost in climb with the descents at cruise power.  I have even had ATC request that I slow down my arrival for traffic.  I have experimented with using the spoilers on final approach as well as the flare. They have very benign handling characteristics.  I am VERY pleased. The spoilers are one of the best upgrades I have made to the aircraft.

Jason Seavolt