I bought this teether for my four month old (she's now 9mo) who was just getting her first teeth. She only used this teether a few times a week when her teething was really bad and then maybe for 20 minutes at most each time. Initially I really liked this teether and she did too. The cold 'keys' really seemed to soothe her gums. The problem has arisen recently when she starting chewing on the side areas of the keys where there is different textures of rubber. I noticed her really focusing on one spot on the blue key and noticed that she had managed to CHEW THROUGH IT! If I hadn't been monitoring it she easily could have torn off a piece of the rubber small enough to swallow or large enough to choke on. I have an e-mail into the company and I am waiting a response. For now I wouldn't recommend using this teether, or if you are going to, make sure your child is supervised at all times and that you check the teether for wear, especially in this area, before and after you give it to them.
UPDATE: I quickly received a response from Luv 'n Care/Nuby. They requested I send the teether back to them so their product developers could look at what happened. They reimbursed me for the cost of the teether. Otherwise I have not had other follow up from them.