Let me first simply copy the Kirst description from the New Langwill index .
Kirst, Friederich Gabriel August, (not completely sure) Born Dresden 1750, Died Berlin 29 April 1806. Flute maker in Potsdam from 1772 to 1804. Probably son of Johann Georg Kirst, inspector of municipal waterworks in Dresden. Apprenticed to A Grenser, Dresden 1768/1770. Working for C.F.Freyer in Potsdam. In 1772 he married Freyer's widow after Freyer died and took over his workshop as master. In 1772 he was also granted 'privilegium privatum' to supply the entire Prussian army with woodwind instruments. Nicolai (1779) reported that flötenmacher Kirst (im Holländischen Revier) bekommt Gehalt vom Könige (woodwind instrument maker Kirst (in the Dutch quarter)receives a salary from the king). There were a number of apprentices in his workshop; J.G. Martin, I.C.H.Müller, A.F.Piering and J.W..Weisse. In 1804 the workshop was taken over by his stepson J.G.Freyer, this changed later to Freyer and Martin. It is most likely both from the extant instruments and form the fact that the workshop was in Potsdam that there was a cooperation between Kirst and Quantz.
So far a slightly reorganized copy from the Langwill index.
The Kirst 415 is a copy of the original owned by Christoph Huntgeburth, the well known player and conservatory teacher in Berlin. The original is a bit too low and has a slightly problematic intonation, as many originals do. I have first, as I always do made a precise copy of this original and then recalculated the pitch a little bit. I retuned as I always do such that now the flute is easy to play.
It is a traverso that is at the same time extremely powerful and beautifully flexible with respect to dynamics. I would say that it is as powerful as the traverso's nowadays acquired for this reason but it can be played piano easily and beautifully as well!
As this is a second half eighteenth century instrument as one would expect the third octave is easy although it needs a few special fingerings to be in tune.
Even though this is a second half eighteenth century flute the professional players owning one are inclined to play everything on it because it certainly has that possibility.
 The New Langwill Index. Tony Bingham London, ISBN 0-946113-04-1