Instruct: Classify Amazon reviews into positive or negative sentiment
Query: great, while it lasts

I can't understand how they get away with still selling these , there is obviously a huge flaw with the recharging unit. I have just thrown away my third, which lasted just over a year, but has been not charging properly for half that time. The other two lasted less time ! I keep trying as I think when it works it does a great job and I prefer it to flossing. I give up now though .