Buy a pre assembled kit and you toss it in your car, pack ...whatever and will probably have to learn to use them when you need them the most. Not the optimal situation.
You are very right about this on both counts, the other being your more vested in something you build yourself.
I am of the opinion of 'rigorous testing'. I go through mini-bic, Mg blocks, rotate whistles, use button compasses as primaries, and always start my fire pit with something other than a lighter. I sleep in my hammock in the winter on my patio and I run sleep in my tent with the grass sprinklers going off every hour to see how dry I stay.
If you don't beat the hell of it and test its limits, it's not worth buying.