I'm currently having a cost segregation done on my STR and I use the STR loophole.
I am trying to see if qualifying for REPS in the future (probably difficult to do with 3 LTR duplexes+ 1 STR) and purchasing a duplex ($600kish) and doing a cost seg, will be as beneficial as the STR cost seg where I put in significant improvements (the duplex will probably be outdated with minimal improvements).