Hello,
First post on this forum 
Has anyone tried to use EFIdroid, to dual boot ubports and an android os?
Like you say TWRP is a good option, that has saved my ass recently while playing around installing different OS’s. My last install was UT-ubports, which I backed up before returning to Lineageos, as its still missing to many apps that I want/need ie encrytped txt and torbrowser to start with (So interested to see anbox working on ubports for FP2, got it working on my laptop in (K)ubuntu 16.04 and it works well for x86 supporting apps like spotify!)! But I still want to be able to play with UT from time to time, without the stress of re-installing, every time.
So getting to my second question, as ubports requires their own recovery, and TWRP (unless (I assume) you use the one-time mode)) removes it, what is this process exactly
Do you mean you re-install every time you want to use UT? or just part of the process after you have recovered the original image via TWRP, that installs Ubuntu recovery pand then the update?
One thing I just saw while trying to find more info on EFIdroid, is that it can handle multiple recoveries! Im not very technical, more of a system breaker than maker 
and there isn’t much info out there that I can find for EFIdroid.
So does any one with more experience than me know if its possible to install UT through EFIdroid? and if so enabling dual boot while preserving both Ubuntu recovery and TWRP?
If/ when this is possible, combined with anbox being usable on a FP2, suddenly UT becomes a real day to day phone! And that is personally my goal, a non-android based OS.