First of all, the price for this program is very reasonable for which the author must be applauded but the effects of the program on my music is mixed.
With CD quality music (16 bit, 44 kHz) enabling Bitperfect had a noticeable effect on the music. Basically it produced a very pleasing atmosphere to the music. Listening to Verdis Requiem the recording became more alive, and I felt like I was transported from a recording into the concert hall. This was with upsampling enabled, which I believe is beneficial to standard resolution music.
With high resolution files, however, say 24 bit, 192 kHz, it had an opposite effect. The music felt more dead, like the magic was taken out of it. The sound of piano was muddied. I feel that at high resolution there should be no effect on the sound as iTunes is bit perfect on its own, but there was definitely an effect and it was not a positive one.
Which leads me to a mixed conclusion and three stars. As far as up sampling, it is a form of digital processing, and to my mind, is no different from enabling artificial surround sound on an inexpensive receiver. In other words, opposite to the audiophile goal of pure signal path. The psychoacoustic effect on standard resolution files is pleasing, but an artifice. That pleasing effect is probably worth the small fee for this program if most of your music files are CD quality or less.