I can't speak for pure4j, but I would be very wary about suggesting Frege at my workplace to (what I'm assuming are) Java programmers.
I feel like some Java programmers would have almost as much culture shock with something like Haskell as some of the php programmers at IMVU apparently did.
Fair point, but it might almost be worth it just to suggest it just to see what the opposition is like -- if there isn't much, or any, go with Frege; otherwise, fall back to pure4j. I'd imagine framing the decision as picking from two choices would improve the odds of at least one being selected.
I feel like some Java programmers would have almost as much culture shock with something like Haskell as some of the php programmers at IMVU apparently did.