I have one of those 5.11 belt bags like pictured above. I do like it except for one thing. The retention buckles that you pull to take up slack in the straps and whatnot do not "bite" the straps hard enough. Just by picking up the bag with the weight of the gun in it, the straps slide through and totally lose your fitment. Also, if you're planning on wearing it a little more loose and casual (not drawn tight like out for a jog), be prepared to have to retighten it a few times.
You say no straps/buckles/etc, but have you looked at the Maxpedition versipacks or the 5.11 push pack? Thats what I use, and the one compartment has a zipper and is lined with heavy velcro so you can secure your gun with any kind of straps or holster. Its pretty quick for an off-body carry.