Product review (4 stars): Far better than a hole in your wall
A bit bulky and kindof a bit of a headache to deal with, but since the dryer location isn't ideal and I'm not going to put a hole in the wall, this thing does great.  A bit of maintenance keeping it filled with water.  A washer repairman came to my place and told me that even hi-budget sort of places sometimes just use this instead of having a vent, and people are happy with it.  Works well- in the dry montana climate I don't mind a little moisture escaping into the bedroom- I make sure I put the vent out in the open when it's in use, so as to not fill the tighter closet space with so much humidity, but don't have any molding issues in this climate.