Which nebulite should I mount on my weapon?

glad to know i made the right choice then :3 bought a freaking A-rank nebulite from a friend for 1B, it's +2 second invincibility, and trying to legend my overall and get it to +4 or +5 second invincibility without nebulite.

this DrK ain't going down after seduce+1/1, no-oh >

I once had +2 and +1 on my overall. Not only did they not stack, i got the +1 bonus instead of the +2. So i'm not sure nebulite will stack with potential.