These preconstruction brackets do help with preliminary speaker and wiring location, but the plastic straps are a bit on the flimsy side. Even when the drywallers were using a proper measure of care, they broke a strap for one of the ceiling brackets. Luckily, we were able to salvage the ring (for 70-RT speakers). I'll use a touch of construction adhesive and glue to ring to the backside of the drywall (and the straps to keep potential vibrations at bay) so I can use the ring when I install the speaker. The rectangular bracket straps survived drywall install, probably because they're on a wall and not the ceiling. I'll likely add some adhesive to all the brackets--on the straps and on the frames. The only drawback I see with these is if the person hanging the drywall doesn't trim tight to the frame and the frame slides around in the opening. While the speaker cam locks would lock to the frame well, the frame (and speaker) could still slip and move within the opening. BTW, I have two Polk 70-RTs installed in our living room ceiling and installed them without the preconstruction brackets. Install was a breeze and speakers sound great. I thought I would try the preconstruction brackets in our basement finish and basically spent what one of the 70-RTs cost. There's less guess work on the speaker layout/install side of things, but I could have easily installed the speakers without the brackets.
Conclusion: good idea if properly executed, a little pricey for the purpose it serves.