My site, http://idogenealogy.net, is fairly new but the spam comments were running about 15-25 per day. I checked each one and bad repeaters were added to a blocked IP form offered by my hosting company.
However, over a two-three week period more and more comments were slipping through as genuine comments and were spam. I started looking for a different plugin and found this one.
I have not rece'd a SINGLE spam since I installed it -- and deactivated & deleted the other one.
This has saved me at least an hour or more a week. I can't imagine what time it would save on an active site.