Great value compared to official Sonicare heads
The bristles are nice and soft and clean well.  They do become frayed after a few weeks of use.  I would say that they last less than half as long as the Sonicare heads.  But they cost much less, so they still work out to be a better value in the long run.  I did not have any problems with the heads falling off that others have mentioned.  In fact, I use the same brush handle for both children (one uses the red heads and the other uses the blue heads), so we're switching the heads all the time and they have not loosened with use.
Rating: 4 stars