Product review (4 stars): Does the job, but not perfect...
This P-tec vent cover does the job and looks decent once installed, however, it is made kind of cheaply and may not work for all applications.  I used this to replace a louvered dryer vent cover that kept getting clogged with lint and would stick open creating a draft in cold weather.  First of all, the components of this vent cover were just thrown into a box with no packing material, so the metal pipe arrived dented and partially smashed.  The metal pipe is very thin-walled, so it was not difficult to bend it back into shape.  Being that there aren't any installation instructions and the description really doesn't specify, my original intention was to just use the plastic vent cover piece on the existing 4" metal duct that is on my house.  This was not possible because the plastic vent cover is designed to snap on to the included metal pipe, which is just slightly smaller than a regular 4" metal duct.  The included metal pipe will slide snugly inside a regular 4" metal duct and then the plastic vent cover snaps on to the end of it.  Also, I did have to position the vent cover with the top slightly further out from the wall than the bottom for the lid to close completely with no air movement.  This is probably because of the slope on my existing dryer vent pipe, but wanted to mention it.

Overall, it looks decent and functions as advertised once installed.  It has reduced the cold air draft compared to the louvered vent and seems less likely to become clogged with lint.  The current price ($14+) seems a little steep for what you get, but could be okay as long as it holds up over time.  The dryer vent location on our house is somewhat weather protected, so I think it should be alright, but with the lightweight plastic materials I could see there being possible issues if it were installed somewhere with greater exposure to the elements.