What is the mechanism of APTES mono-layer formation on glass substrates?
Here's two links (1, 2) that show the simple scheme on forming monolayers. The essential figure is also shown here. 



For the second part of your question... I can only point out this article that describes which properties change, if you make the molecules more bulky or add chloride, etc. I would guess that APTES has well known properties and they are "neutral" regarding common applications.