MLB,
I understand what you are saying and I agree with you. I now have full confidence that my weapon was designed and tested to function properly as is. But the bendable guide rod did raise some concerns the first time I took the pistol apart and put it back together. "If I can bend it with my fingers, what will weapon recoil do to it over time?" type questions. But as I learned more, I gained faith in it.
Similar story with my RRA M4. Every time you shoot it, the recoil spring (in the stock) goies 'sproinnnnggg!' as the weapon cycles. Sounds super cheap, but it works and works well.
My 2c - if the polymer guide rod ever fails, then maybe it would be worth spending the $70 for a metal replacement. I don't think its worth $70 just to swap out a perfectly good polymer guide rod though.