Product review (4 stars): Works...but maybe not as easy to install
Within minutes we could detect a rise in laundry room temperature (it is February) after I installed a vent closure for both the dryer AND for a shower vent from the same room.  That more than offsets any of the complications with the installation, to me.  The end of the hard or flex vent pipes exiting the house do not "neatly" fit with the female receiving end (against the house) of these closure units, at least neither of mine did.  A descriptive of possible options - Plan B, Plan C, etc. - would have been helpful upfront.  It took a while to adapt then secure the unit to the pipes then to the house.  In other words, this may not be a 10 minute installation effort.  Be prepared to shim the siding a bit and to have to "customize" the feeding vent pipe into the closure unit.

But winters will be warmer and summers will be cooler in that room...amen.