I had the same desire early on playing Nisha. But cos of the same strong advice I’d gotten from friends who were both far more experienced Nishas than me, I chose against rushing my build in order just to reach her zerking skill.
Nisha’s middle branch capstone skill (tier six) is a single point into One For Each of Ya which is a relatively small potatoes skill compared to real gunzerking in Sal’s method ~ with a point in OFEOY, Nisha can only zerk two of the same pistols but the game doesn’t even give you an option to change from the two pistols grip (which can take up more than 50% of your monitor / vision) to the traditional one pistol grip if you prefer it for a particular situation ~ the only solution is to respec Nisha out of OFEOY completely which can be a real pain.
As well, there’s a strange output to Nisha’s two pistols gunfire too ~ you don’t get two guns’ worth of firepower simultaneously cos the dual pistols with OFEOY will only shoot one at a time [e.g. both triggers can’t be pulled simultaneously for double powered shots] which totally sucks & comes close to defeating the whole purpose of her skill OFEOY’s zerking alltogether. I think it’s safe to say most Nishas surely trial the OFEOY cos it’s there but sticking with it is another story.
I first built my whole Nisha tree to level 65 with similar weightings in the three branches and then selectively topped off other skills or opted into the point needed for some single-pointers (like OFEOY). I had counseling early in the game from two friends who are experienced Nishas specifically and in TPS generally and that really helped - both gave great advice giving subtle suggestions that never acted as spoilers. I’ve been tracking my Nisha build and gameplay in another string here as she levels up thru the game & will return to finish her off with a post on my level 70 build when I reach it (am now 68), I’ll do a summary post with my favored lvl 70 build, top gear & a few pointers for beginner Nishas to keep in mind. Have fun