Product review (2 stars): Avoid it. Get a real metal Dryerbox!
I installed this since my mom bought it before talking to me. This cheap, styrene thing is over $40 and worth $5. It cracks if you breathe on it too hard. I had to glue it together because the thin, brittle plastic cracked.

Save yourself some money and headache and get the real thing with good instructions (2x4 retrofit box, RB-400 is $30). Amazon doesn't carry them, though. We've installed both the 4" and 6" versions of the Dryerbox with no problems. You want RETROFIT version unless you plan to rip out your drywall.