Actually I have two of those 'bumpy' blue balls bouncing around in my dryer as I type. lol I've had them for about a year or so now.

Here's my assesment of them:

Pros:

Helps clothes dry faster

Fluffs up towels and coats better

Easy to use and clean

Makes it so you can use LESS fabric softner


Cons:

Make a bit of a muffled banging noise when using (doesn't bother me but it may some people)

Doesn't do a thing for static! (I get horrible static pokes in the winter so this is a biggie for me)

Get stuck in the sleeves of clothes. When I get all done hanging stuff up and realize I have one 'bumpy' ball missing I have to go through all the shirt sleeves to find the errant ball. LOL

Sometimes I wish I had another set of them for the larger items I dry.



Despite the downsides, I use them every time I dry clothes now and am able to use less fabric softner but I still have to use some for the static.