Having considered such additional safety equipment, and how or when I would have ever thought to use it, during more than 5000 hours of GA flying, the answer comes back to me: NEVER! Certainly one can speculate on conditions of aircraft failure where such an additional safety feature would be reassuring, but I assure you that in the real world of qualified, well prepared flight, of well maintained aircraft, failures which would justify a whole aircraft chute are so rare that I don't think they are statistically relevent.
There is quite a cost, weight penalty, and cabin space penalty for retrofits, along with recurring inspection costs.
Add to that the STC approved installation in the C150 has just been AD'd. The AD itself says that there are 6 such equipped aircraft in the US, and none in Canada.
It is my opinion that there are a wide variety of things a pilot/owner can do to assure a safe flight. If you are feeling insecure about the reliabilty of the aircraft you fly, get to know it by participating in some maintenance. Either you'll get to be much more reassured, and stop worrying; or realize that the particular aircraft is defective and either fix it, or ground it!
Pilot DAR