I found that I had a reasonably good squat to start with, so far on 5/3/1, I've found that my upper body has improved dramatically (especially my overhead press). 5/3/1 has such a variety of assistance too, generally if you're doing it with a powerlifting focus, you do it as 3/5/1 or use Karl's Method. I've just finished my first cycle on BBB, and I like it simply for doing more of the 4 lifts. I also BB curl and do dips in addition.
I like the routine as an intermediate (according to STRSD scale), I'll probably stick with it for a few years. I too have noticed other intermediate lifters heading straight onto Sheiko or Cube etc.
Yeah I've seen the guys who own PTC gyms bash generic routines like 5/3/1, again it's not something you'd probably run if you were laser focused on powerlifting.