Product review (4 stars): Requires aluminum foil tape, but worth it!
Yes, it's true that the seams aren't airtight and you'll need to tape them up with aluminum foil tape. Not that big of a deal, honestly, since you'll need to tape the sliding connection point between the parts anyway, and you should be using the same tape on other connections of your duct. Other than that, it installed easily and definitely fit the bill! My washer/dryer are now sitting about 2" back from where they used to be with a conventional duct.