Theyre great little brackets & do the job well. Theyre plastic but strong & capable of achieving plenty of horizontal & vertical movement. For extra strength, I fixed mine into brick using 8mm Rawl plugs (brown) instead of the supplied red ones (those supplied with the brackets) & used a washer to ensure that when i tightened the screw into the wall it didnt split the plastic.
Just to note, The DX-1's take an M6 bolt into the rear to hold them onto the bracket, so I had to make the hole in the bracket slightly larger to fit an M6 - the brackets come with M5 bolts hence holes are M5 size & need widening. Additionally, you'll have to turn the brackets upside down, since at the back of the speakers there is the plastic casing for the binding post housing that sticks out, fouling the placement of the bracket its intended way around, this still works fine however.