The ability to directly measure electron density is quite an old technique. STMs and AFMs have been doing this since the very beginning.. I agree with the researcher's quote in the article that it's good to develop a complementary technique(FEEM) abd at best that's its contribution. I'd be happy to hear what else it contributes. though I don't quite agree with his or the editors spelling!
;) "it's always good to have complimentary approaches,"