If you use TX trim, the controller will see the trim as the new neutral each time you power it up in that same flight mode and you'll have to keep adding trim.
I have read Do Not Use TX Trims and I have read it is fine to use TX trims and or sub trims in many different FBL threads. Even employees of HH / E flite / Blade will controdict each other and what is posted on the WWW or written in the User's Guides.
First hand experience. Note I have seen most of these flights and in addation my son was the one who set up my Tarot ZYX-S in my Blade 400 for me just over a week ago.
Note: This current discusion about Tx Sub. trims and software Monitor and servo centering is about a Blade 450 with a Copter X .
My son has a Blade 450 which he converted to Tarot XYZ-S and uses John's Software . He finished his tuning perhaps a month ago and now has close to 60 flights on it and he has used some Aft cyclic trim on his DX 7 Tx since day one. His Tarot XZ-S does not see the Trans trim as a new zero each time.
But you should use servo trim in the FBL controller.
Most likely the "simple" fact (detail) I have over looked. As I posted FBL per Tarot and Coptrer X plus computer GUI all new to me.
I have flown Blade mCPXs and 130 X but those are B N F with no users tuning in the mCPX and limited tuning on the 130X.