strong arms

I have a stress crack in one of the arms. Because I can't send it in for free warranty repair, I installed the UAV BITS strong arms for removable prop guards, am I'm happy to report that after 19 flights (11 of those without prop guards), the crack has stayed stable. I think it'll stay stable...

Very interested in avoiding stress cracks. I've gotten the strong arms from this same company, but is that a permanent or temporary fix? Is a subframe worth getting? Does it affect the P3's performance at all? I've seen it mentioned in other threads.