When I first ran across these recordings, I dismissed them as another "romantic atrocity" commited against the music of Bach.
While some period purists, myself usually included, would cry foul at the inclusion of a modern grand piano in these concerti, I think it useful to remember that Bach was not ignorant of the pianoforte and its capabilities. In 1747, Bach was invited to the Court of Prussian Emperor Frederick the Great at Berlin where he was asked to test out the Silbermann pianofortes (the pianoforte was invented in 1709. Bach's prowess on the instrument so impressed the Emperor, that he asked Bach to improvise on a subject of his (the Emperor's) own invention, from which came the Musical Offering.
The modern piano is completely capable of overpowering a baroque chamber orchestra and to Hewitt's credit, she never exceeds the bounds of good taste and dignity by descending to the bombast that could potentially ruin this music and turn the soloist into the proverbial bull in a china shop. That is not to say that her interpretations are sterile and uninteresting; The very nature of the piano provides for a timbral and dynamic expressiveness unattainable on the harpsichord, and the soloist uses these effects to their best within the limits of the genre-conforming the piano to Bach and not Bach to the piano.
The 5th Brandenburg concerto, while obviously not 'authentic' is played with such grace and deference to the music and the other soloists that it becomes a joy to listen to. The flautist and violinist in the Brandenburg and triple concerti as well as the flautists in the 5th concerto, although playing modern instruments, are nonetheless gracious in their interpretation, once again conforming their instruments and technique to the music and not the other way around.
The Orchestra's performance is excellent. Though not perfoming on period instruments, they maintain the clear, precise timbre of a baroque orchestra. While the literal meaning of concerto may mean contest, the baroque concerto is less a contest and more of a cooperation of solo and orchestral forces than its romantic descendant which is almost a battle at times. The result is that neither soloist nor orchestra usurps the other's place in the music.
In the end, This performance, while not a period performance, is definitely not a romantic interpretation either and deserves to be heard if for no other reason than that it is a new take on these musical gems.