Very Durable!
I bought this item 6 months ago. This may be unhygienic, but I've only used 1 head from the package the entire time. (Sorry Dentists)  It is very durable.  Currently, the bristles have a slight curvature.  None are bent at an angle and all are full length; no breaks.  I had no issues attaching the head to the unit.  Easy opening package can be used to store new heads. It will likely be at least another month until I pull out my 2nd head. :)  Oh, and in case you're wondering, yes, I do have a very healthy mouth according to my Dentist.  Great product!
Rating: 5 stars