Very good advice here from Red.
I'm a huge Sato fan myself, but Nidra is easier to make, has the same triggers and also does not have the penalty for low Synchro like Sato.
You should definitely keep the Savitri, though. In Episode 2, using V101, V502 and SMARTLINK at the same time is very important. This, however, leaves you with only one more Slot which might be filled with a V801 (when you are not using "Black Odoshi Violet Nimaidou", a level 150 armor).
It is hard to give HUney high ATA for many levels using only one Unit - her ATA base is pretty low - so your Mag will still have a use. In many Areas in Episode 2, Hell (and therefore, ATA) is more important than high ATP. However, until you get the necessary equips for using Hell effectively - most importantly, V502 - a 150 POW Mag is the way to go.