Saw this review, and ordered mine last week. $11 shipped, arrived within a week. Great idea if you keep your uppers seperated for storage or trasport. Mine snaps into place securely and does what it advertises.
http://www.militarymorons.com/weapons/ar.access3.html#topstop
http://www.militarymorons.com/weapons/ar.access3.html#topstop