The above photograph shows the kework of a Ewen
McDougall silver Flute which is constructed with an "inline G mechanism"
In this instance the mechanism is indeed inline, but on careful scrutiny
The two "G" keys can be seen to be nearly in inline with the other keys, the centres of which are all in line.
Offset keys are more commonly associated with closed hole keywork as on the above flute. This is by no means true of all flutes - there are plenty of open hole flutes with offset G and also closed hole flutes with in-line G
The advantages of offset keys are that the mechanism is simpler and the keys are positioned more naturally for Human fingers.A Split E Mechanism can easily be fitted to offset G mechanism, but is complex on the in line mechanism There are few disadvantages. However the in-line G mechanism which has a more complicated mechanism (albeit perhaps a little lighter in weight) is by far the most popular for various reasons which are probably aesthetic or commercial rather than beneficial to the flute or flute player.
For more information on this subject go to The
FAQ on the Larry Krantz Web Site
The above photograph and notes are as accurate as my knowledge of the subject permits