Product review (3 stars): Functional, cheap (good and bad), seems to be only option available unfortunately
This item does what it's intended for, and does it moderately well. It allows you to redirect the heat from your dryer into your home instead of the outside in the cold months. Unfortunately, there is a significant design flaw, which makes little sense to me. I'll get into that at the end.

First, it's cheap. It's molded plastic that is folded in half to make a tube shape and fit the flapper inside the box. Unfortunately, mine doesn't fold completely and the natural stress in the plastic makes it slightly not circular. This isn't a problem for connecting tubing, but it is a problem for the flapper, as it doesn't seat fully in the outside-flowing tube, so it allows cold air in. Second on the cheap scale are the zip ties it comes with. They are a step up from your standard single-use zip ties, as they have a lever to unlatch and expand them. However, the lever is impossible to push without taking the whole thing off and getting a pair of pliers on both sides of the zip, so it's pointless. Use a standard metal worm clamp instead.

The lint trap is useless: Take a stocking or cut off pantyhose and fit it over the end instead of the lint filter, like you probably do on your washer outlet. It's a much better filter.

Now to the biggest design flaw, which I can only partially try to explain: There is a hole in the flapper, with a small flimsy inner flapper covering it. The effect is that when the flapper is up, to redirect hot air into your home, much of it is still pushed outside. And when it is in the other position, moving air will pull it open and suck out inside air, and/or push hot air into your home (I'm not sure which, as it's winter now and I don't want to test it right now). My only guess why this inner flapper exists at all is that it is to make up for the poorly closing main flapper, so you don't get stagnant moist air hanging out in the section between the "heat keeper" and your outside vent. The effect it has is that the heat keeper doesn't rully redirect air, is leaky, and forces you to mount it in one specific orientation, otherwise the inner flapper will hang open and let in outside air.

TLDR: It works, but leaks and could be better, and unfortunately there doesn't seem to be a better option made anymore.