The EFRs use some very... uh, "legacy" compressor designs and never really impressed me in that regard. The turbines were ambitious and interesting, the overall turbo product line was comprehensive, but it seems like BW ran out of steam or didn't have the resources to develop a proper modern compressor for them.
Thats odd, I have never heard that critique of the them but I also have not looked for any.
To me, the strong points of them was the strength of the packaged accessories and varieties of housings available. Good internal gates and CBVs that can stand up to the performance of the turbo.