Works fine, but overpriced
These work fine for what they are, but ultimately, it's constructed of cheap plastic. The benefit is that you can set your speaker placement and run your wire before drywall is done, and it gives the drywallers a way to locate the speaker hole as well as a mud ring. Also, instead of your speaker's locking tabs clamping directly to crumbly drywall, they now clamp to a solid plastic ring that reinforces the drywall. Other than the price, my only gripe is that the plastic straps extending off the ring are not long enough for unlimited placement between 24" on-center joists. Meaning if you want the speaker close to a joist, the strap on the opposite side won't reach the next joist.