I've used the Chimney cleaning logs before and they do work somewhat to keep the Chimney clean but you still need to clean the Chimney with a brush at least once every year at the end of the heating season to make sure no creosote has built up which can cause a Chimney Fire.
The Chimney cleaning logs burn for around 90 minutes and release an additive that clings to the creosote which cleans it off the chimney pipe.
You can also periodically burn an aluminum soda can in the wood stove which can clean the chimney as well but do make sure that you do actually manually sweep the chimney to full clean it out once in awhile.
Even though those Chimney Sweep logs work I no longer use them because I find it much cheaper and easier to just sweep out the Wood Stove Chimney at the end of the heating season.