How doe's it attach?

It just presses on with a little force, or you can take that little adapter off and thread it directly on the objective lens for a more secure fit.

So I can take it on/off in the field quickly?

Yes, I use mine a TON and keep it on a lanyard around my neck.  It attaches/detaches very quickly if you are using the friction fit adapter.  The only time I thread it onto the NOD is when I'm mounting my 14 behind an optic which isn't very often.  The mil-spec 3x lens is indispensable IMHO.  I even find myself wishing I wouldn't have sold my 5x a couple years ago despite the fact that it wasn't used very often then.

Please share some of your uses!

I use mine for surveillance, ( i'm in LE) coyote hunting, general use around my property; I live in a rural setting.