I would like to mount my Comp ML2 on an M4 flat top for 1/3 cowitnessing.  Between the Larue and the ARMS mount (with tall spacer) - which is better?  

Many prefer the LaRue over the ARMS, due to the ARMS' habit of screws loosening up. That said, I'm still using an ARMS 22M68 with a cantilever spacer to secure my Aimpoint ML2 to my rifle. Once I put some Loc-Tite on the screws, it has never loosened again.

M4Madness beat me to it, So what he said.

Quoted: M4Madness beat me to it, So what he said.

Umm...I think I would make that a +2!  

Tom  

Quoted: Quoted: M4Madness beat me to it, So what he said. Umm...I think I would make that a +2!   Tom

I have both.

I like the LaRue better.

also like the larue over the arms

I currently use the ARMS with the tall spacer, it gives me a good lower 1/3 co-witness.  BUT it moves around on me.  I noticed I was having to re-sight in my gun everytime I went shooting.  At first I blamed it on me removing the aimpoint/mount and remounting it between shoots.  So I stopped doing that, but then realized that I could actually move the whole assembly a little bit.  So today I took the entire mount apart and put it back together, everything is damned tight now.  I was curious if this cured my problems so I pushed on the aimpoint.  It still moves!  I know it moved because when co-witnessing the dot sits right on top of the front sight post.  When I pushed on it the dot moves between the post and wing.  
Is this due to there being 3 pieces to the mount?  The throw lever piece, the spacer and the ring?  I dunno

I will be ordering a Larue shortly.

I know other people, even friends of mine who have never had a problem with theirs, so nothing against ARMS in general, just mine.

arms offset spacer, degressed all 3 screws before assy and no loctite. 2.5 thousands rounds no signs of loose screws.

LaRue - End of discussion.