I have both a G10 and FRCP Manix 2 and I an tell you without a doubt that the polymer cage is more than durable. I'm a flicker, I open and close my knives so much that it's annoying to the point of insanity for some people. I'd bet my FRCP has been opened and closed thousands if not 10,000 times. I carry it on me when I'm at home and it's always in my basketball shorts even while I sleep! I was actually flicking it when I started reading this. My G10 has been opened a ton too but at work my hands have something to do (mechanic) so I'm not so bad. I actually broke both springs on a Benchmade Griptillian doing this so much. My Manix 2s are still going strong! The only thing that broken was the pocket clip when I got it caught and snapped it off. I've been missing my Manix 2 at work, I just have to get around to ordering a new clip.
I trust my Manix 2s over all my other knives to function perfectly, as much as I trust my Cold Steel Tri-Ad folders. The CS seems to have a tougher lock but the Spydies have better ergos, so they're even. The CBBL is a tough lock though. I went through quite a few liner and frame locks because of my habit to flick. I've had both fail on me (the only locks that ever have) and will never buy another of either. They are made to be cheap to manufacture, not strong. They're just not a locks that should be on serious knives that will or can be used hard. The CBBL on my Manix 2s have seen their way through road grime, metal shavings, brake dust, dirt, and any thing else I could throw at it.
I trust the CBBL (and its polymer cage) completely and I'm sure my Manix 2s will to continue to function for many years to come! Buy the Manix 2 with confidence!