Kegelstatt is a German word meaning ‘playground for skittles’, skittles being a precursor of bowling. The (unproven) legend is that Mozart composed the trio while playing skittles.
The first movement of this work which I have both played and recorded more thanI can remember has a tempo of 6 beats, not two. This is of course contrary to what many say but is the result of a considerble amount of study, both of Mozarts works (there is a piano trio with the same kind of ‘written-out” turns, obviously to be played more slowly ) and the question of why each turn is written out? If the original manuscript has only the turn marked and not written, some support may be made for the movement in two(however the manuscript has them written out as well). Finally, after the initial difficulty with a slow tempo, (things must be played really in-time, which the “turns” are never ) and all phrases must be finished, tapered and artistically rendered, the first movement emerges as slow and rather stately, offering a contast to the other movements which are quicker. The proportions of the performance are than more generous, the work not presented as a flip quick melodious plaything.
I would add that this is not the “given” for this movement, but I am convinced it is the more musical and logical. It is also considerably more difficult then throwing turns off as they usually are. Try playing them exactly intime and you are probably “on” to the reason for the “in two” tempo usually played for the first movement.
The big trap of playing it in two is that it makes the first and second movements frequently in similar tempo, which for me is to be avoided.