I have used these dryer balls several times since they arrived and the main pro so far has been that they do cut my drying time. I would not say 40% but probably close to 25 maybe even 30%. I actually use a coin dryer and normally my clothes are still a little damp after one dryer cycle and I have to pay to use another cycle to finish them or hang dry them for a few hours. With these balls I no longer have to waste that extra dollar because my clothes come out dry or 99% dry in just one cycle so for me this is a win. I like that I can put a few drops of my favorite essential oil on each ball and throw 4 in for a medium load or all 6 for a large and that is it.
These are very loud in the dryer so be prepared it sounds like when you dry tennis shoes since they are bouncing around the whole cycle. I had no issues with the wool coming off or leaving any particles on my clothes. For the most part my clothes come out static free but I do have one garment(a nightgown) that I normally wash and dry and with my old dryer sheets it would come out mostly static free. With these balls this one garment always has static but it is not enough for me to discard these balls because they are saving me money nearly 4 dollars a week every week sometimes more.
The only thing I wish is that these balls retained the oil scent longer because I have to re-apply my oil every load but I do use a light scented grapefruit oil instead of something really strong so that may be the reason why. Overall I am impressed with these dryer balls and have made them a new permanent staple in my laundry routine. (15 dollar price point at time of review) I received this set of dryer balls for free in exchange for my honest review. Amazon Link