Wife bought a s7 and I have found it is running a custom firmware few questions.

About Phone : 64G Dual Sim Gold
Model number
SM-G930F
6.0.1
Baseband:G930FVPU1APB5
Kernel:3.10.72dpi@SWDD5616 #1 tue Jun7 19:53:44 CST 2016
Build:LRX22G.G930FZCU1AOD9
Custom build version: SEPF_SM_930F_5.0.2_0008
Phone INFO shows: Bootloader :Unknown
PDA Blank CSC Blank
Kernel Version:3.10.72 dpi@SWDD5616 #1 32-bit
Build Description: full_hexing6580_we_I-user 6.0.1 LMY471 1465299661 test-keys

My Questions are where is this firmware from, is it safe to use ?
Seems to burn through the battery fast.
Smart switch didn't work correctly, what could I try as alternative (Old phone is S5)
Is there a better custom firmware I could use?
Could this have been done to get around a blocked IMEI ?
Would it be safe to Flash a Stock firmware, will it still work, what firmware would I use ?
Location is Australia and Network is Telstra.
Thanks