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I do not see a glass as half empty or half full. I see container that wants to maim me, with contents that will drown or poison me. 
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I'm an Engineer as well. Half empty or half full?.....My opinion is that the glass was not designed for the correct capacity!
The design of the Quickjack makes me nervous. Every corner of that 'box' is a flexible joint. The single lock bar does little to make that trapezoid into a solid, geometrically stable stand. Four lock bars may strengthen it sufficiently in case of a malfunction.
And this statement in the manual sums up it's intended use and limitations:
>>>Do not work under an elevated Vehicle unless properly rated Vehicle Jack Stands are used and place under the factory approved Lifting Points.<<<<So there you go, it's only designed to raise and lower the car and not safely support it for working underneath it. And since it raises/lowers at an angle (not straight up/down) it may be difficult to lower a car evenly down onto 4 jack stands without side loading them.
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And the only access is front or rear and sliding into a "box".
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And the only EXIT is at the front/rear! Scary!
It is what it is.... designed to raise and lower a car from the ground to jackstands.
Instead of jackstands (or in addition to), I often use block platforms under each of the four tires.
And if I'm working under a lifted car, I'll take a wheel/tire under there with me in case the car does fall.... hoping it'll keep ME from getting crushed.
But thanks for the post! The product does has an intended use but most are likely to not fully realize it's limitations until after they buy it.
And if you do buy one, be sure to wear your safety glasses while using it! (that's in the manual too).
