My hammock came with adjustment buckles.  In the setup instructions it tell you if the webbing does not go through straight it will slip and they are correct.  Occasionally I will be in a hurry and make a fast adjustment and not pull in line with the straps and when I set on the hammock it is a letdown. I have never had them slip when they were straight.
I started off without carabineers.  That required removing the straps from the buckels to feed it through the eye in the strap.  Carabineers make set up much easier and faster but what works even better is Dutch clips.  I also have sewn some Dutch hooks on to my hammock to make attaching my under quilt faster and snugger.