We bought two sets of two each and have already been using two of the new brushes. They are working well and were easy to install on the unit. We are very satisfied with them.
Unlike the original head that came with my brush this product has extra vibration at the lower part resulting to my battery going down due to the extra work. You will need extra battery power to operate.
They don't fit my battery operated Spinbrush perfectly. You're suppose to turn them to secure them in place. On mine they don't rotate as much as I thought the would so the angle isn't perfectly parallel to the handle, but it actually doesn't matter. They work very well.
The replacement brush is soft, works as designed, and most importantly keeps my teeth smooth & clean. I've used the Crest Spinbrush for several years and have had no issues.